8-K 1 mab04op1_sep.txt SEPTEMBER 8K UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington D. C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): September 27, 2004 MASTR ASSET BACKED SECURITIES TRUST Mortgage Pass-Through Certificates, Series 2004-OP1 Trust (Exact name of registrant as specified in its charter) New York (governing law of 333-106982-19 54-2150433 Pooling and Servicing Agreement) (Commission 54-2150434 (State or other File Number) IRS EIN jurisdiction of Incorporation) c/o Wells Fargo Bank, N.A. 9062 Old Annapolis Road Columbia, MD 21045 (Address of principal executive offices) (Zip Code) Registrant's telephone number, including area code: (410) 884-2000 (Former name or former address, if changed since last report) Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below): [ ] Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) [ ] Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) [ ] Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act(17 CFR 240.14d-2(b)) [ ] Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act(17 CFR 240.13e-4(c)) ITEM 8.01 Other Events On September 27, 2004 a distribution was made to holders of MASTR ASSET BACKED SECURITIES TRUST, Mortgage Pass-Through Certificates, Series 2004-OP1 Trust. ITEM 9.01 Financial Statements and Exhibits (c) Exhibits Exhibit Number Description EX-99.1 Monthly report distributed to holders of Mortgage Pass-Through Certificates, Series 2004-OP1 Trust, relating to the September 27, 2004 distribution. Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. MASTR ASSET BACKED SECURITIES TRUST Mortgage Pass-Through Certificates, Series 2004-OP1 Trust (Registrant) By: Wells Fargo Bank, N.A. as Trustee By: /s/ Beth Belfield as Assistant Vice President By: Beth Belfield as Assistant Vice President Date: 10/5/2004 INDEX TO EXHIBITS Exhibit Number Description EX-99.1 Monthly report distributed to holders of Mortgage Pass-Through Certificates, Series 2004-OP1 Trust, relating to the September 27, 2004 distribution. EX-99.1

MASTR Asset Backed Securitizations Mortgage Pass-Through Certificates Record Date: 78/31/042004 Distribution Date: 89/2527/042004 MABS Series: 2004-~~OPT1~~OP1 Contact: Customer Service - CTSLink Wells Fargo Bank, N.A. Securities Administration Services 7485 New Horizon Way Frederick, MD 21703 Telephone: (301) 815-6600 Fax: (301) 815-6660 Certificateholder Distribution Summary Certificate Certificate Beginning Class Pass-Through Certificate Interest Principal Class CUSIP Description Rate Balance Distribution Distribution A-1 57643LCE4 SEN 1.~~73000~~89500% ~~211~~201,~~922~~516,~~958~~341.0478 ~~305~~350,~~522~~050.2668 10,~~406~~164,~~616~~795.2636 A-2 57643LCF1 SEN 1.~~73000~~89500% ~~114~~109,~~859~~758,~~772~~942.2334 ~~165~~190,~~589~~660.5043 54,~~100~~321,~~829~~757.8981 A-3 57643LCG9 SEN 1.~~71000~~87500% ~~162~~153,~~729~~200,~~201~~136.5844 ~~231~~263,~~889~~312.1174 97,~~529~~978,~~065~~029.1422 M-1 57643LCH7 MEZ 12.~~97000~~13500% 42,151,000.00 6982,~~197~~493.8902 0.00 M-2 57643LCJ3 MEZ 2.~~55000~~71500% 34,333,000.00 7285,~~957~~446.6226 0.00 M-3 57643LCK0 MEZ 2.~~75000~~91500% 10,538,000.00 2428,~~149~~158.5841 0.00 M-4 57643LCL8 MEZ 3.~~00000~~16500% 8,158,000.00 2023,~~395~~668.0040 0.00 M-5 57643LCM6 MEZ 3.~~15000~~31500% 8,838,000.00 2326,~~199~~856.7547 0.00 M-6 57643LCN4 MEZ 4.~~20000~~36500% 6,799,000.00 2327,~~796~~204.50 0.00 M-7 57643LCP9 MEZ 5.~~20000~~36500% 7,138,000.00 3035,~~931~~104.3309 0.00 CE MAB4OPT1C OC 0.00000% 7,818,296.32 2,~~697~~411,~~885~~263.5843 0.00 R MAB4OP1R2 RES 0.00000% 0.00 0.00 0.00 P MAB4OPT1P Pre-pay 0.00000% 100.00 ~~431~~296,~~323~~475.9276 0.00 Totals ~~615~~590,~~285~~248,~~328~~816.1788 43,~~096~~820,~~838~~694.0419 2522,~~036~~464,~~511~~582.2939

Certificateholder Distribution Summary (continued) Current Ending Cumulative Realized Certificate Total Realized Class Loss Balance Distribution Losses A-1 0.00 ~~201~~191,~~516~~351,~~341~~546.7842 10,~~712~~514,~~138~~846.5204 0.00 A-2 0.00 ~~109~~105,~~758~~437,~~942~~184.3453 54,~~266~~512,~~419~~418.3924 0.00 A-3 0.00 ~~153~~145,~~200~~222,~~136~~107.4422 98,~~760~~241,~~954~~341.2596 0.00 M-1 0.00 42,151,000.00 6982,~~197~~493.8902 0.00 M-2 0.00 34,333,000.00 7285,~~957~~446.6226 0.00 M-3 0.00 10,538,000.00 2428,~~149~~158.5841 0.00 M-4 0.00 8,158,000.00 2023,~~395~~668.0040 0.00 M-5 0.00 8,838,000.00 2326,~~199~~856.7547 0.00 M-6 0.00 6,799,000.00 2327,~~796~~204.50 0.00 M-7 0.00 7,138,000.00 3035,~~931~~104.3309 0.00 CE 0.00 7,818,296.32 2,~~697~~411,~~885~~263.5843 0.00 R 0.00 0.00 0.00 0.00 P 0.00 100.00 ~~431~~296,~~323~~475.9276 0.00 Totals 0.00 ~~590~~567,~~248~~784,~~816~~234.8849 2926,~~133~~285,~~349~~276.3358 0.00 All distributions required by the Pooling and Servicing Agreement have been calculated by the Certificate Administrator on behalf of the Trustee.

Principal Distribution Statement Original Beginning Scheduled Unscheduled Face Certificate Principal Principal Realized Class Amount Balance Distribution Distribution Accretion Loss (1) A-1 240,738,000.00 ~~211~~201,~~922~~516,~~958~~341.0478 0.00 10,~~406~~164,~~616~~795.2636 0.00 0.00 A-2 129,838,000.00 ~~114~~109,~~859~~758,~~772~~942.2334 0.00 54,~~100~~321,~~829~~757.8981 0.00 0.00 A-3 183,503,000.00 ~~162~~153,~~729~~200,~~201~~136.5844 0.00 97,~~529~~978,~~065~~029.1422 0.00 0.00 M-1 42,151,000.00 42,151,000.00 0.00 0.00 0.00 0.00 M-2 34,333,000.00 34,333,000.00 0.00 0.00 0.00 0.00 M-3 10,538,000.00 10,538,000.00 0.00 0.00 0.00 0.00 M-4 8,158,000.00 8,158,000.00 0.00 0.00 0.00 0.00 M-5 8,838,000.00 8,838,000.00 0.00 0.00 0.00 0.00 M-6 6,799,000.00 6,799,000.00 0.00 0.00 0.00 0.00 M-7 7,138,000.00 7,138,000.00 0.00 0.00 0.00 0.00 CE 7,817,754.23 7,818,296.32 0.00 0.00 0.00 0.00 R 0.00 0.00 0.00 0.00 0.00 0.00 P 100.00 100.00 0.00 0.00 0.00 0.00 Totals 679,851,854.23 ~~615~~590,~~285~~248,~~328~~816.1788 0.00 2522,~~036~~464,~~511~~582.2939 0.00 0.00 (1) Amount Does Not Include Excess Special Hazard, Bankruptcy, or Fraud Losses Unless Otherwise Disclosed. Please Refer to the Prospectus Supplement for a Full Description.

Principal Distribution Statement (continued) Total Ending Ending Total Principal Certificate Certificate Principal Class Reduction Balance Percentage Distribution A-1 10,~~406~~164,~~616~~795.2636 ~~201~~191,~~516~~351,~~341~~546.7842 0.~~83707741~~79485393 10,~~406~~164,~~616~~795.2636 A-2 54,~~100~~321,~~829~~757.8981 ~~109~~105,~~758~~437,~~942~~184.3453 0.~~84535300~~81206723 54,~~100~~321,~~829~~757.8981 A-3 97,~~529~~978,~~065~~029.1422 ~~153~~145,~~200~~222,~~136~~107.4422 0.~~83486448~~79138819 97,~~529~~978,~~065~~029.1422 M-1 0.00 42,151,000.00 1.00000000 0.00 M-2 0.00 34,333,000.00 1.00000000 0.00 M-3 0.00 10,538,000.00 1.00000000 0.00 M-4 0.00 8,158,000.00 1.00000000 0.00 M-5 0.00 8,838,000.00 1.00000000 0.00 M-6 0.00 6,799,000.00 1.00000000 0.00 M-7 0.00 7,138,000.00 1.00000000 0.00 CE 0.00 7,818,296.32 1.00006934 0.00 R 0.00 0.00 0.00000000 0.00 P 0.00 100.00 1.00000000 0.00 Totals 2522,~~036~~464,~~511~~582.2939 ~~590~~567,~~248~~784,~~816~~234.8849 0.~~86820211~~83515876 2522,~~036~~464,~~511~~582.2939

Principal Distribution Factors Statement Original Beginning Scheduled Unscheduled Face Certificate Principal Principal Class (2) Amount Balance Distribution Distribution Accretion A-1 240,738,000.00 ~~880~~837.~~30538610~~07741104 0.00000000 4342.~~22797506~~22347681 0.00000000 A-2 129,838,000.00 ~~884~~845.~~63910589~~35299635 0.00000000 3933.~~28610954~~28577004 0.00000000 A-3 183,503,000.00 ~~886~~834.~~79314006~~86447873 0.00000000 5143.~~92866133~~47628769 0.00000000 M-1 42,151,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-2 34,333,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-3 10,538,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-4 8,158,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-5 8,838,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-6 6,799,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-7 7,138,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 CE 7,817,754.23 1000.06934089 0.00000000 0.00000000 0.00000000 R 0.00 0.00000000 0.00000000 0.00000000 0.00000000 P 100.00 1000.00000000 0.00000000 0.00000000 0.00000000 (2) All Classes are per $1,000 denomination

Principal Distribution Factors Statement (continued) Total Ending Ending Total Realized Principal Certificate Certificate Principal Class Loss (3) Reduction Balance Percentage Distribution A-1 0.00000000 4342.~~22797506~~22347681 ~~837~~794.~~07741104~~85393424 0.~~83707741~~79485393 4342.~~22797506~~22347681 A-2 0.00000000 3933.~~28610954~~28577004 ~~845~~812.~~35299635~~06722631 0.~~84535300~~81206723 3933.~~28610954~~28577004 A-3 0.00000000 5143.~~92866133~~47628769 ~~834~~791.~~86447873~~38819104 0.~~83486448~~79138819 5143.~~92866133~~47628769 M-1 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 M-2 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 M-3 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 M-4 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 M-5 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 M-6 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 M-7 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 CE 0.00000000 0.00000000 1,000.06934089 1.00006934 0.00000000 R 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 P 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 (3) Amount Does Not Include Excess Special Hazard, Bankruptcy, or Fraud Losses Unless Otherwise Disclosed. Please Refer to the Prospectus Supplement for a Full Description.

Interest Distribution Statement Beginning Payment of Original Current Certificate/ Current Unpaid Current Face Certificate Notional Accrued Interest Interest Class Amount Rate Balance Interest Shortfall Shortfall A-1 240,738,000.00 1.~~73000~~89500% ~~211~~201,~~922~~516,~~958~~341.0478 ~~305~~350,~~522~~050.2668 0.00 0.00 A-2 129,838,000.00 1.~~73000~~89500% ~~114~~109,~~859~~758,~~772~~942.2334 ~~165~~190,~~589~~660.5043 0.00 0.00 A-3 183,503,000.00 1.~~71000~~87500% ~~162~~153,~~729~~200,~~201~~136.5844 ~~231~~263,~~889~~312.1173 0.00 0.00 M-1 42,151,000.00 12.~~97000~~13500% 42,151,000.00 6982,~~197~~493.8902 0.00 0.00 M-2 34,333,000.00 2.~~55000~~71500% 34,333,000.00 7285,~~957~~446.6325 0.00 0.00 M-3 10,538,000.00 2.~~75000~~91500% 10,538,000.00 2428,~~149~~158.5841 0.00 0.00 M-4 8,158,000.00 3.~~00000~~16500% 8,158,000.00 2023,~~395~~668.0040 0.00 0.00 M-5 8,838,000.00 3.~~15000~~31500% 8,838,000.00 2326,~~199~~856.7547 0.00 0.00 M-6 6,799,000.00 4.~~20000~~36500% 6,799,000.00 2327,~~796~~204.50 0.00 0.00 M-7 7,138,000.00 5.~~20000~~36500% 7,138,000.00 3035,~~931~~104.3309 0.00 0.00 CE 7,817,754.23 0.00000% 7,818,296.32 0.00 0.00 0.00 R 0.00 0.00000% 0.00 0.00 0.00 0.00 P 100.00 0.00000% 100.00 0.00 0.00 0.00 Totals 679,851,854.23 ~~967~~1,~~628~~112,954.5598 0.00 0.00

Interest Distribution Statement (continued) Remaining Ending Non-Supported Total Unpaid Certificate/ Interest Realized Interest Interest Notional Class Shortfall Losses (4) Distribution Shortfall Balance A-1 (0.0001) 0.00 ~~305~~350,~~522~~050.2668 0.00 ~~201~~191,~~516~~351,~~341~~546.7842 A-2 0.00 0.00 ~~165~~190,~~589~~660.5043 0.00 ~~109~~105,~~758~~437,~~942~~184.3453 A-3 0.00 0.00 ~~231~~263,~~889~~312.1174 0.00 ~~153~~145,~~200~~222,~~136~~107.4422 M-1 0.00 0.00 6982,~~197~~493.8902 0.00 42,151,000.00 M-2 0.00 0.00 7285,~~957~~446.6226 0.00 34,333,000.00 M-3 0.00 0.00 2428,~~149~~158.5841 0.00 10,538,000.00 M-4 0.00 0.00 2023,~~395~~668.0040 0.00 8,158,000.00 M-5 0.00 0.00 2326,~~199~~856.7547 0.00 8,838,000.00 M-6 0.00 0.00 2327,~~796~~204.50 0.00 6,799,000.00 M-7 0.00 0.00 3035,~~931~~104.3309 0.00 7,138,000.00 CE 0.00 0.00 2,~~697~~411,~~885~~263.5843 0.00 7,818,296.32 R 0.00 0.00 0.00 0.00 0.00 P 0.00 0.00 ~~431~~296,~~323~~475.9276 0.00 100.00 Totals (0.0001) 0.00 43,~~096~~820,~~838~~694.0419 0.00 (4) Amount Does Not Include Excess Special Hazard, Bankruptcy, or Fraud Losses Unless Otherwise Disclosed. Please Refer to the Prospectus Supplement for a Full Description.

Interest Distribution Factors Statement Beginning Payment of Original Current Certificate/ Current Unpaid Current Face Certificate Notional Accrued Interest Interest Class (5) Amount Rate Balance Interest Shortfall Shortfall A-1 240,738,000.00 1.~~73000~~89500% ~~880~~837.~~30538610~~07741104 1.~~26910691~~45407322 0.00000000 0.00000000 A-2 129,838,000.00 1.~~73000~~89500% ~~884~~845.~~63910589~~35299635 1.~~27535467~~46844861 0.00000000 0.00000000 A-3 183,503,000.00 1.~~71000~~87500% ~~886~~834.~~79314006~~86447873 1.~~26368021~~43492330 0.00000000 0.00000000 M-1 42,151,000.00 12.~~97000~~13500% 1000.00000000 1.~~64166663~~95708334 0.00000000 0.00000000 M-2 34,333,000.00 2.~~55000~~71500% 1000.00000000 2.~~12500015~~48874989 0.00000000 0.00000000 M-3 10,538,000.00 2.~~75000~~91500% 1000.00000000 2.~~29166635~~67208294 0.00000000 0.00000000 M-4 8,158,000.00 3.~~00000~~16500% 1000.00000000 2.~~50000000~~90125031 0.00000000 0.00000000 M-5 8,838,000.00 3.~~15000~~31500% 1000.00000000 23.~~62500000~~03874972 0.00000000 0.00000000 M-6 6,799,000.00 4.~~20000~~36500% 1000.00000000 34.~~50000000~~00125018 0.00000000 0.00000000 M-7 7,138,000.00 5.~~20000~~36500% 1000.00000000 4.~~33333287~~91791678 0.00000000 0.00000000 CE 7,817,754.23 0.00000% 1000.06934089 0.00000000 0.00000000 0.00000000 R 0.00 0.00000% 0.00000000 0.00000000 0.00000000 0.00000000 P 100.00 0.00000% 1000.00000000 0.00000000 0.00000000 0.00000000 (5) All Classes are per $1,000 denomination

Interest Distribution Factors Statement (continued) Remaining Ending Non-Supported Total Unpaid Certificate/ Interest Realized Interest Interest Notional Class Shortfall Losses (6) Distribution Shortfall Balance A-1 (0.~~00000000~~00000004) 0.00000000 1.~~26910691~~45407322 0.00000000 ~~837~~794.~~07741104~~85393424 A-2 0.00000000 0.00000000 1.~~27535467~~46844861 0.00000000 ~~845~~812.~~35299635~~06722631 A-3 0.00000000 0.00000000 1.~~26368021~~43492335 0.00000000 ~~834~~791.~~86447873~~38819104 M-1 0.00000000 0.00000000 1.~~64166663~~95708334 0.00000000 1000.00000000 M-2 0.00000000 0.00000000 2.~~12499985~~48875018 0.00000000 1000.00000000 M-3 0.00000000 0.00000000 2.~~29166635~~67208294 0.00000000 1000.00000000 M-4 0.00000000 0.00000000 2.~~50000000~~90125031 0.00000000 1000.00000000 M-5 0.00000000 0.00000000 23.~~62500000~~03874972 0.00000000 1000.00000000 M-6 0.00000000 0.00000000 34.~~50000000~~00125018 0.00000000 1000.00000000 M-7 0.00000000 0.00000000 4.~~33333287~~91791678 0.00000000 1000.00000000 CE 0.00000000 0.00000000 ~~345~~308.~~09726203~~43428420 0.00000000 1000.06934089 R 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 P 0.00000000 0.00000000 ~~4313239~~2964757.~~20000000~~60000000 0.00000000 1000.00000000 (6) Amount Does Not Include Excess Special Hazard, Bankruptcy,or Fraud Losses Unless Otherwise Disclosed. Please Refer to the Prospectus Supplement for a Full Description.

CERTIFICATEHOLDER ACCOUNT STATEMENT CERTIFICATE ACCOUNT Beginning Balance 0.00 Deposits Payments of Interest and Principal 2826,~~864~~139,~~664~~841.8016 Liquidations, Insurance Proceeds, Reserve Funds 0.00 Proceeds from Repurchased Loans 0.00 Other Amounts (Servicer Advances) 0.00 Realized Loss (Gains, Subsequent Expenses & Recoveries) ~~(4,716~~456.~~17)~~88 Prepayment Penalties ~~431~~296,~~323~~475.9276 Total Deposits 2926,~~291~~436,~~272~~773.5580 Withdrawals Reimbursement for Servicer Advances 0.00 Payment of Service Fee ~~157~~151,~~923~~497.22 Payment of Interest and Principal 2926,~~133~~285,~~349~~276.3358 Total Withdrawals (Pool Distribution Amount) 2926,~~291~~436,~~272~~773.5580 Ending Balance 0.00

SERVICING FEES Gross Servicing Fee ~~153~~147,~~821~~562.3223 Trustee Fee -Wells Fargo Bank, NA 43,~~101~~934.9099 Supported Prepayment/Curtailment Interest Shortfall 0.00 Net Servicing Fee ~~157~~151,~~923~~497.22

OTHER ACCOUNTS Beginning Current Current Ending Account Type Balance Withdrawals Deposits Balance Reserve Fund 1,000.0001 0.00 0.0100 1,000.01 Reserve Fund 0.00 0.00 0.00 0.00

LOAN STATUS STRATIFICATION/CREDIT ENHANCEMENT STATEMENT DELINQUENCY STATUS DELINQUENT BANKRUPTCY FORECLOSURE REO Total No of Loans No of Loans No of Loans No of Loans No of Loans Principal Balance Principal Balance Principal Balance Principal Balance Principal Balance 0-29 Days 810 12 0 912 ~~870~~1,~~863~~041,271.3379 ~~278~~466,~~241~~265.8474 0.00 1,~~149~~507,~~105~~537.1753 30 Days 5852 01 31 0 6154 107,~~268~~841,~~114~~709.7443 0235,959.0049 ~~722~~278,~~030~~241.7584 0.00 108,~~990~~355,~~145~~910.4976 60 Days 1523 0 65 0 2128 23,~~787~~743,~~493~~402.2475 0.00 ~~640~~1,~~012~~021,258.5382 0.00 34,~~427~~764,~~505~~661.7757 90 Days 712 13 2126 13 3044 1,~~010~~995,~~680~~920.7919 50275,~~043~~420.1493 23,~~874~~613,~~459~~883.9634 91325,~~958~~684.8658 46,~~027~~210,~~142~~909.7504 120 Days 0 0 0 0 0 0.00 0.00 0.00 0.00 0.00 150 Days 0 0 0 0 0 0.00 0.00 0.00 0.00 0.00 180+ Days 0 0 0 0 0 0.00 0.00 0.00 0.00 0.00 Totals 8087 914 3134 13 ~~121~~138 1413,~~066~~581,~~288~~032.7737 ~~920~~1,~~906~~552,652.4721 45,~~514~~379,~~745~~649.0874 91325,~~958~~684.8658 1920,~~593~~839,~~899~~018.1890 No of Loans No of Loans No of Loans No of Loans No of Loans Principal Balance Principal Balance Principal Balance Principal Balance Principal Balance 0-29 Days 0.~~207361~~267380% 0.~~025920~~053476% 0.000000% 0.~~233281~~320856% 0.~~147484~~183327% 0.~~047121~~082091% 0.000000% 0.~~194606~~265418% 30 Days 1.~~503370~~390374% 0.~~000000~~026738% 0.~~077760~~026738% 0.000000% 1.~~581130~~443850% 1.~~738947~~380617% 0.~~000000~~041543% 0.~~122279~~048987% 0.000000% 1.~~861226~~471147% 60 Days 0.~~388802~~614973% 0.000000% 0.~~155521~~133690% 0.000000% 0.~~544323~~748663% 0.~~472073~~659066% 0.000000% 0.~~108389~~179804% 0.000000% 0.~~580462~~838870% 90 Days 0.~~181441~~320856% 0.~~025920~~080214% 0.~~544323~~695187% 0.~~025920~~080214% 01.~~777605~~176471% 0.~~171163~~351403% 0.~~008475~~048491% 0.~~486802~~636263% 0.~~015574~~057340% 01.~~682013~~093497% 120 Days 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 150 Days 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 180+ Days 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% 0.000000% Totals 2.~~073613~~326203% 0.~~233281~~374332% 0.~~803525~~909091% 0.~~025920~~080214% 3.~~136340~~689840% 2.~~382184~~391086% 0.~~155959~~273361% 0.~~764591~~947145% 0.~~015574~~057340% 3.~~318307~~668932%

OTHER INFORMATION Current Period Class A Insufficient Funds 0.00 Principal Balance of Contaminated Properties 0.00 Periodic Advance ~~231~~247,~~628~~523.2368 Class M-1 83,621,854.23 12.30001120% 83,622,396.32 14.~~16731282~~72784752% 7.~~141226~~423771% 0.000000% Class M-2 49,288,854.23 7.24994040% 49,289,396.32 8.~~35061332~~68100826% 56.~~816700~~046839% 0.000000% Class M-3 38,750,854.23 5.69989682% 38,751,396.32 6.~~56526455~~82502154% 1.~~785349~~855987% 0.000000% Class M-4 30,592,854.23 4.49992951% 30,593,396.32 5.~~18313556~~38820814% 1.~~382129~~436813% 0.000000% Class CE 100.00 0.00001471% 100.00 0.~~00001694~~00001761% 1.~~324576~~376984% 0.000000% Class R-II 100.00 0.00001471% 100.00 0.~~00001694~~00001761% 0.000000% 0.000000% Class P 0.00 0.00000000% 0.00 0.00000000% 0.~~000017~~000018% 0.000000% Please Refer to the Prospectus Supplement for a Full Description of Loss Exposure

COLLATERAL STATEMENT Collateral Description Mixed Fixed & Arm Weighted Average Gross Coupon 7.~~466104~~471951% Weighted Average Net Coupon 7.~~166104~~171951% Weighted Average Pass-Through Rate 7.~~158104~~163951% Weighted Average Maturity(Stepdown Calculation ) ~~347~~346 Beginning Scheduled Collateral Loan Count 3,~~993~~858 Number Of Loans Paid In Full ~~135~~118 Ending Scheduled Collateral Loan Count 3,~~858~~740 Beginning Scheduled Collateral Balance ~~615~~590,~~285~~248,~~328~~816.1889 Ending Scheduled Collateral Balance ~~590~~567,~~248~~784,~~816~~234.8949 Ending Actual Collateral Balance at 31-~~Jul~~Aug-2004 ~~590~~567,~~478~~985,~~772~~964.3679 Monthly P &I Constant 4,~~349~~181,~~587~~756.5410 Special Servicing Fee 0.00 Prepayment Penalties ~~431~~296,~~323~~475.9276 Realized Loss Amount ~~4,716~~(456.1788) Cumulative Realized Loss 54,~~207~~259.2329 Ending Scheduled Balance for Premium Loans ~~590~~567,~~248~~784,~~816~~234.8949 Scheduled Principal ~~521~~506,~~433~~497.9935 Unscheduled Principal 2421,~~515~~958,~~077~~085.3005

Miscellaneous Reporting Net Monthly Excess Cashflow 12,~~622~~410,~~602~~806.0484 Extra Principal Ditribution Amount 0-456.0088 OC Amount 7,818,~~296~~297.3200 OC Deficiency Amount 0.00 OC Release Amount 0-456.0088 OC Target Amount 7,818,~~296~~297.3200 Stepdown NO Trigger Event NO Credit Enhancement Percentage 2021.~~441459~~208523%

Group Level Collateral Statement Group Group 1 Group 2 Group 3 Collateral Description Fixed 15/30 & ARM Fixed 15/30 & ARM Fixed 15/30 & ARM Weighted Average Coupon Rate 7.~~571656~~575743 9.~~464943~~464983 7.~~516557~~518296 Weighted Average Net Rate 7.~~271656~~275743 9.~~164965~~164988 7.~~216557~~218296 Weighted Average Maturity ~~347~~346 ~~347~~346 ~~347~~346 Beginning Loan Count ~~728~~715 3 1,~~176~~126 Loans Paid In Full 1311 0 5049 Ending Loan Count ~~715~~704 3 1,~~126~~077 Beginning Scheduled Balance 9795,~~703~~778,~~158~~319.7003 256,~~379~~243.3788 ~~168~~160,~~609~~129,~~291~~610.6990 Ending scheduled Balance 9594,~~778~~315,~~319~~224.0379 256,~~243~~107.8833 ~~160~~151,~~129~~427,~~610~~839.9060 Record Date 0708/31/2004 0708/31/2004 0708/31/2004 Principal And Interest Constant ~~708~~696,~~869~~538.2601 2,157.67 1,~~184~~126,~~877~~049.2373 Scheduled Principal 9291,~~390~~878.3708 ~~135~~136.4955 ~~128~~122,~~742~~798.8128 Unscheduled Principal 1,~~832~~371,~~449~~216.3016 0.00 8,~~350~~578,~~937~~973.9802 Scheduled Interest ~~616~~604,~~478~~659.8993 2,~~022~~021.1812 1,~~056~~003,~~134~~251.4245 Servicing Fees 2423,~~425~~944.7859 64.0906 4240,~~152~~032.3438 Master Servicing Fees 0.00 0.00 0.00 Trustee Fee ~~651~~638.3553 1.71 1,~~124~~067.0556 FRY Amount 0.00 0.00 0.00 Special Hazard Fee 0.00 0.00 0.00 Other Fee 0.00 0.00 0.00 Pool Insurance Fee 0.00 0.00 0.00 Spread Fee 1 0.00 0.00 0.00 Spread Fee 2 0.00 0.00 0.00 Spread Fee 3 0.00 0.00 0.00 Net Interest ~~592~~580,~~053~~076.1881 1,~~958~~955.0935 1962,~~013,982~~151.1051 Realized Loss Amount 0.00 0.00 0.00 Cumulative Realized Loss 0.00 0.00 0.00 Percentage of Cumulative Losses 0.0000 0.0000 0.0000 Prepayment Penalties 0.00 0.00 0.00 Special Servicing Fee 0.00 0.00 0.00 Pass-Through Rate 7.~~263656~~267743 9.~~156943~~156983 7.~~208557~~210296

Group Level Collateral Statement Group Group 4 Group 5 Group 6 Collateral Description Fixed 15/30 & ARM Fixed 15/30 & ARM Fixed 15/30 & ARM Weighted Average Coupon Rate 7.~~571709~~580028 8.~~114032~~114026 7.~~460081~~461849 Weighted Average Net Rate 7.~~271709~~280028 7.~~814019~~814027 7.~~160080~~161849 Weighted Average Maturity ~~347~~346 ~~347~~346 ~~347~~346 Beginning Loan Count ~~387~~380 4 ~~596~~573 Loans Paid In Full 73 0 2324 Ending Loan Count ~~380~~377 4 ~~573~~549 Beginning Scheduled Balance 5352,~~662~~622,~~591~~855.9360 ~~306~~305,~~146~~880.6871 9086,~~364~~304,~~111~~244.1844 Ending scheduled Balance 5251,~~622~~999,~~855~~089.6067 305,~~880~~662.7194 8682,~~304~~606,~~244~~382.4443 Record Date 0708/31/2004 0708/31/2004 0708/31/2004 Principal And Interest Constant ~~387~~380,~~147~~602.3666 2,286.04 ~~632~~605,~~807~~434.9274 Scheduled Principal 48,~~549~~200.4139 ~~215~~217.9777 7168,~~038~~777.3006 Unscheduled Principal ~~991~~575,~~186~~565.9254 500.00 3,~~988~~629,~~828~~084.4495 Scheduled Interest ~~338~~332,~~597~~402.9527 2,~~070~~068.0727 ~~561~~536,~~769~~657.6268 Servicing Fees 13,~~415~~155.6473 76.5447 2221,~~591~~576.0406 Master Servicing Fees 0.00 0.00 0.00 Trustee Fee ~~357~~350.7781 2.04 ~~602~~575.4336 FRY Amount 0.00 0.00 0.00 Special Hazard Fee 0.00 0.00 0.00 Other Fee 0.00 0.00 0.00 Pool Insurance Fee 0.00 0.00 0.00 Spread Fee 1 0.00 0.00 0.00 Spread Fee 2 0.00 0.00 0.00 Spread Fee 3 0.00 0.00 0.00 Net Interest ~~325~~318,~~182~~895.3373 1,~~993~~989.5376 ~~539~~514,~~178~~506.5526 Realized Loss Amount 0.00 0.00 0.00 Cumulative Realized Loss 0.00 0.00 0.00 Percentage of Cumulative Losses 0.0000 0.0000 0.0000 Prepayment Penalties 0.00 0.00 0.00 Special Servicing Fee 0.00 0.00 0.00 Pass-Through Rate 7.~~263709~~272028 7.~~806032~~806026 7.~~152080~~153849

Group Level Collateral Statement Group Group 7 Group 8 Group 9 Collateral Description Fixed 15/30 & ARM Fixed 15/30 & ARM Fixed 15/30 & ARM Weighted Average Coupon Rate 7.~~372005~~374040 6.~~700031~~699999 7.~~325065~~339045 Weighted Average Net Rate 7.~~072006~~074039 6.~~400010~~399966 7.~~025065~~039045 Weighted Average Maturity ~~345~~344.00 ~~345~~344.00 ~~345~~344.00 Record Date 0708/31/2004 0708/31/2004 0708/31/2004 Principal And Interest Constant ~~645~~630,~~740~~377.9154 597.83 ~~785~~737,~~103~~711.3288 Beginning Loan Count ~~525~~511 1 ~~573~~545 Loans Paid In Full 1411 0 2820 Ending Loan Count ~~511~~500 1 ~~545~~525 Beginning Scheduled Balance 9087,~~125~~763,~~956~~958.9498 9291,~~073~~989.6186 ~~114~~106,~~165~~995,~~618~~713.0849 Ending Scheduled Balance 8785,~~763~~760,~~958~~262.9896 91,~~989~~905.8664 ~~106~~101,~~995~~021,~~713~~759.4913 Scheduled Principal 9291,~~066~~065.7112 8384.7522 8883,~~211~~339.1888 Unscheduled Principal 21,~~269~~912,~~931~~630.2590 0.00 75,~~081~~890,~~693~~614.4148 Scheduled Interest ~~553~~539,~~674~~312.2042 ~~514~~513.0861 ~~696~~654,~~892~~372.1400 Servicing Fee 2221,~~531~~941.4801 23.0200 2826,~~541~~748.3993 Master Servicing Fee 0.00 0.00 0.00 Trustee Fee ~~600~~585.8306 0.61 ~~761~~713.1131 Fry Amount 0.00 0.00 0.00 Special Hazard Fee 0.00 0.00 0.00 Other Fee 0.00 0.00 0.00 Pool Insurance Fee 0.00 0.00 0.00 Spread 1 0.00 0.00 0.00 Spread 2 0.00 0.00 0.00 Spread 3 0.00 0.00 0.00 Net Interest ~~531~~516,~~142~~786.8235 490.4500 ~~668~~626,~~350~~909.8576 Realized Loss Amount 0.00 0.00 ~~4,716~~(456.1788) Cumulative Realized Loss 0.00 ~~491~~0.0600 4,~~716~~259.1729 Percentage of Cumulative Losses 0.0000 0.~~5314~~0000 0.~~0036~~0033 Prepayment Penalties 0.00 0.00 0.00 Special Servicing Fee 0.00 0.00 0.00 Pass-Through Rate 7.~~064005~~066040 6.~~392031~~391999 7.~~017065~~031045

Group Level Collateral Statement Group Total Collateral Description Mixed Fixed & Arm Weighted Average Coupon Rate 7.~~466104~~471951 Weighted Average Net Rate 7.~~166104~~171951 Weighted Average Maturity ~~347~~346.00 Record Date 0708/31/2004 Principal And Interest Constant 4,~~349~~181,~~587~~756.5410 Beginning Loan Count 3,~~993~~858 Loans Paid In Full ~~135~~118 Ending Loan Count 3,~~858~~740 Beginning Scheduled Balance ~~615~~590,~~285~~248,~~328~~816.1889 Ending Scheduled Balance ~~590~~567,~~248~~784,~~816~~234.8949 Scheduled Principal ~~521~~506,~~433~~497.9935 Unscheduled Principal 2421,~~515~~958,~~077~~085.3005 Scheduled Interest 3,~~828~~675,~~153~~258.5575 Servicing Fee ~~153~~147,~~821~~562.3223 Master Servicing Fee 0.00 Trustee Fee 43,~~101~~934.9099 Fry Amount 0.00 Special Hazard Fee 0.00 Other Fee 0.00 Pool Insurance Fee 0.00 Spread 1 0.00 Spread 2 0.00 Spread 3 0.00 Net Interest 3,~~674~~523,~~331~~761.9053 Realized Loss Amount ~~4,716~~(456.1788) Cumulative Realized Loss 54,~~207~~259.2329 Percentage of Cumulative Losses 0.~~0008~~0006 Prepayment Penalties 0.00 Special Servicing Fee 0.00 Pass-Through Rate 7.~~158104~~163951

Filing Compare · MASTR ASSET BACKED SECURITIES TRUST 2004-OPT1