8-K 1 mabs04opt1.txt AUGUST 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): August 25, 2004 MASTR ASSET BACKED SECURITIES TRUST Mortgage Pass-Through Certificates, Series 2004-OPT1 Trust (Exact name of registrant as specified in its charter) New York (governing law of 333-106982-19 Pooling and Servicing Agreement) (Commission 54-2150433 (State or other File Number) 54-2150434 jurisdiction IRS EIN 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 August 25, 2004 a distribution was made to holders of MASTR ASSET BACKED SECURITIES TRUST, Mortgage Pass-Through Certificates, Series 2004-OPT1 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-OPT1 Trust, relating to the August 25, 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-OPT1 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: 8/30/04 INDEX TO EXHIBITS Exhibit Number Description EX-99.1 Monthly report distributed to holders of Mortgage Pass-Through Certificates, Series 2004-OPT1 Trust, relating to the August 25, 2004 distribution. EX-99.1

MASTR Asset Backed Securitizations Mortgage Pass-Through Certificates Record Date: 67/3031/04 Distribution Date: 78/2625/04 MABS Series: 2004-OPT1 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.~~58000~~73000% ~~221~~211,~~394~~922,~~345~~958.8504 ~~301~~305,~~219~~522.3126 910,~~471~~406,~~387~~616.8126 A-2 57643LCF1 SEN 1.~~58000~~73000% ~~119~~114,~~676~~859,~~993~~772.0523 ~~162~~165,~~827~~589.1950 45,~~817~~100,~~220~~829.8289 A-3 57643LCG9 SEN 1.~~56000~~71000% ~~168~~162,~~352~~729,~~861~~201.4958 ~~226~~231,~~154~~889.0111 59,~~623~~529,~~659~~065.9114 M-1 57643LCH7 MEZ 1.~~82000~~97000% 42,151,000.00 6669,~~059~~197.9889 0.00 M-2 57643LCJ3 MEZ 2.~~40000~~55000% 34,333,000.00 7072,~~954~~957.8762 0.00 M-3 57643LCK0 MEZ 2.~~60000~~75000% 10,538,000.00 2324,~~593~~149.4158 0.00 M-4 57643LCL8 MEZ 23.~~85000~~00000% 8,158,000.00 20,~~021~~395.0900 0.00 M-5 57643LCM6 MEZ 3.~~00000~~15000% 8,838,000.00 2223,~~831~~199.5075 0.00 M-6 57643LCN4 MEZ 4.~~05000~~20000% 6,799,000.00 23,~~711~~796.5150 0.00 M-7 57643LCP9 MEZ 5.~~05000~~20000% 7,138,000.00 3130,~~040~~931.3933 0.00 CE MAB4OPT1C OC 0.00000% 7,818,296.32 2,~~845~~697,~~294~~885.3158 0.00 R MAB4OP1R2 RES 0.00000% 0.00 0.00 0.00 P MAB4OPT1P Pre-pay 0.00000% 100.00 ~~309~~431,~~299~~323.4792 0.00 Totals ~~635~~615,~~197~~285,~~596~~328.7117 4,~~103~~096,~~007~~838.04 1925,~~912~~036,~~268~~511.5429

Certificateholder Distribution Summary (continued) Current Ending Cumulative Realized Certificate Total Realized Class Loss Balance Distribution Losses A-1 0.00 ~~211~~201,~~922~~516,~~958~~341.0478 910,~~772~~712,~~607~~138.1252 0.00 A-2 0.00 ~~114~~109,~~859~~758,~~772~~942.2334 45,~~980~~266,~~048~~419.0139 0.00 A-3 0.00 ~~162~~153,~~729~~200,~~201~~136.5844 59,~~849~~760,~~813~~954.9225 0.00 M-1 0.00 42,151,000.00 6669,~~059~~197.9889 0.00 M-2 0.00 34,333,000.00 7072,~~954~~957.8762 0.00 M-3 0.00 10,538,000.00 2324,~~593~~149.4158 0.00 M-4 0.00 8,158,000.00 20,~~021~~395.0900 0.00 M-5 0.00 8,838,000.00 2223,~~831~~199.5075 0.00 M-6 0.00 6,799,000.00 23,~~711~~796.5150 0.00 M-7 0.00 7,138,000.00 3130,~~040~~931.3933 0.00 CE 0.00 7,818,296.32 2,~~845~~697,~~294~~885.3158 0.00 R 0.00 0.00 0.00 0.00 P 0.00 100.00 ~~309~~431,~~299~~323.4792 0.00 Totals 0.00 ~~615~~590,~~285~~248,~~328~~816.1788 2429,~~015~~133,~~275~~349.5833 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 ~~221~~211,~~394~~922,~~345~~958.8504 0.00 910,~~471~~406,~~387~~616.8126 0.00 0.00 A-2 129,838,000.00 ~~119~~114,~~676~~859,~~993~~772.0523 0.00 45,~~817~~100,~~220~~829.8289 0.00 0.00 A-3 183,503,000.00 ~~168~~162,~~352~~729,~~861~~201.4958 0.00 59,~~623~~529,~~659~~065.9114 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 ~~635~~615,~~197~~285,~~596~~328.7117 0.00 1925,~~912~~036,~~268~~511.5429 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-1 910,~~471~~406,~~387~~616.8126 ~~211~~201,~~922~~516,~~958~~341.0478 0.~~88030539~~83707741 910,~~471~~406,~~387~~616.8126 A-2 45,~~817~~100,~~220~~829.8289 ~~114~~109,~~859~~758,~~772~~942.2334 0.~~88463911~~84535300 45,~~817~~100,~~220~~829.8289 A-3 59,~~623~~529,~~659~~065.9114 ~~162~~153,~~729~~200,~~201~~136.5844 0.~~88679314~~83486448 59,~~623~~529,~~659~~065.9114 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 1925,~~912~~036,~~268~~511.5429 ~~615~~590,~~285~~248,~~328~~816.1788 0.~~90502854~~86820211 1925,~~912~~036,~~268~~511.5429

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 ~~919~~880.~~64852184~~30538610 0.00000000 3943.~~34313573~~22797506 0.00000000 A-2 129,838,000.00 ~~921~~884.~~74088518~~63910589 0.00000000 3739.~~10177929~~28610954 0.00000000 A-3 183,503,000.00 ~~917~~886.~~43928704~~79314006 0.00000000 3051.~~64614698~~92866133 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 3943.~~34313573~~22797506 ~~880~~837.~~30538610~~07741104 0.~~88030539~~83707741 3943.~~34313573~~22797506 A-2 0.00000000 3739.~~10177929~~28610954 ~~884~~845.~~63910589~~35299635 0.~~88463911~~84535300 3739.~~10177929~~28610954 A-3 0.00000000 3051.~~64614698~~92866133 ~~886~~834.~~79314006~~86447873 0.~~88679314~~83486448 3051.~~64614698~~92866133 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.~~58000~~73000% ~~221~~211,~~394~~922,~~345~~958.8504 ~~301~~305,~~219~~522.3126 0.00 0.00 A-2 129,838,000.00 1.~~58000~~73000% ~~119~~114,~~676~~859,~~993~~772.0523 ~~162~~165,~~827~~589.2050 0.00 0.00 A-3 183,503,000.00 1.~~56000~~71000% ~~168~~162,~~352~~729,~~861~~201.4958 ~~226~~231,~~154~~889.0111 0.00 0.00 M-1 42,151,000.00 1.~~82000~~97000% 42,151,000.00 6669,~~059~~197.9889 0.00 0.00 M-2 34,333,000.00 2.~~40000~~55000% 34,333,000.00 7072,~~954~~957.8763 0.00 0.00 M-3 10,538,000.00 2.~~60000~~75000% 10,538,000.00 2324,~~593~~149.4158 0.00 0.00 M-4 8,158,000.00 23.~~85000~~00000% 8,158,000.00 20,~~021~~395.0900 0.00 0.00 M-5 8,838,000.00 3.~~00000~~15000% 8,838,000.00 2223,~~831~~199.5075 0.00 0.00 M-6 6,799,000.00 4.~~05000~~20000% 6,799,000.00 23,~~711~~796.5150 0.00 0.00 M-7 7,138,000.00 5.~~05000~~20000% 7,138,000.00 3130,~~040~~931.3933 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 ~~948~~967,~~413~~628.2755 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 0.00 0.00 ~~301~~305,~~219~~522.3126 0.00 ~~211~~201,~~922~~516,~~958~~341.0478 A-2 0.00 0.00 ~~162~~165,~~827~~589.1950 0.00 ~~114~~109,~~859~~758,~~772~~942.2334 A-3 0.00 0.00 ~~226~~231,~~154~~889.0111 0.00 ~~162~~153,~~729~~200,~~201~~136.5844 M-1 0.00 0.00 6669,~~059~~197.9889 0.00 42,151,000.00 M-2 0.00 0.00 7072,~~954~~957.8762 0.00 34,333,000.00 M-3 0.00 0.00 2324,~~593~~149.4158 0.00 10,538,000.00 M-4 0.00 0.00 20,~~021~~395.0900 0.00 8,158,000.00 M-5 0.00 0.00 2223,~~831~~199.5075 0.00 8,838,000.00 M-6 0.00 0.00 23,~~711~~796.5150 0.00 6,799,000.00 M-7 0.00 0.00 3130,~~040~~931.3933 0.00 7,138,000.00 CE 0.00 0.00 2,~~845~~697,~~294~~885.3158 0.00 7,818,296.32 R 0.00 0.00 0.00 0.00 0.00 P 0.00 0.00 ~~309~~431,~~299~~323.4792 0.00 100.00 Totals 0.00 0.00 4,~~103~~096,~~007~~838.04 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.~~58000~~73000% ~~919~~880.~~64852184~~30538610 1.~~25123292~~26910691 0.00000000 0.00000000 A-2 129,838,000.00 1.~~58000~~73000% ~~921~~884.~~74088518~~63910589 1.~~25407970~~27535467 0.00000000 0.00000000 A-3 183,503,000.00 1.~~56000~~71000% ~~917~~886.~~43928704~~79314006 1.~~23242677~~26368021 0.00000000 0.00000000 M-1 42,151,000.00 1.~~82000~~97000% 1000.00000000 1.~~56722213~~64166663 0.00000000 0.00000000 M-2 34,333,000.00 2.~~40000~~55000% 1000.00000000 2.~~06666676~~12500015 0.00000000 0.00000000 M-3 10,538,000.00 2.~~60000~~75000% 1000.00000000 2.~~23888878~~29166635 0.00000000 0.00000000 M-4 8,158,000.00 23.~~85000~~00000% 1000.00000000 2.~~45416646~~50000000 0.00000000 0.00000000 M-5 8,838,000.00 3.~~00000~~15000% 1000.00000000 2.~~58333333~~62500000 0.00000000 0.00000000 M-6 6,799,000.00 4.~~05000~~20000% 1000.00000000 3.~~48749963~~50000000 0.00000000 0.00000000 M-7 7,138,000.00 5.~~05000~~20000% 1000.00000000 4.~~34861166~~33333287 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 0.00000000 1.~~25123292~~26910691 0.00000000 ~~880~~837.~~30538610~~07741104 A-2 0.00000000 0.00000000 1.~~25407962~~27535467 0.00000000 ~~884~~845.~~63910589~~35299635 A-3 0.00000000 0.00000000 1.~~23242677~~26368021 0.00000000 ~~886~~834.~~79314006~~86447873 M-1 0.00000000 0.00000000 1.~~56722213~~64166663 0.00000000 1000.00000000 M-2 0.00000000 0.00000000 2.~~06666676~~12499985 0.00000000 1000.00000000 M-3 0.00000000 0.00000000 2.~~23888878~~29166635 0.00000000 1000.00000000 M-4 0.00000000 0.00000000 2.~~45416646~~50000000 0.00000000 1000.00000000 M-5 0.00000000 0.00000000 2.~~58333333~~62500000 0.00000000 1000.00000000 M-6 0.00000000 0.00000000 3.~~48749963~~50000000 0.00000000 1000.00000000 M-7 0.00000000 0.00000000 4.~~34861166~~33333287 0.00000000 1000.00000000 CE 0.00000000 0.00000000 ~~363~~345.~~95289827~~09726203 0.00000000 1000.06934089 R 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 P 0.00000000 0.00000000 ~~3092994~~4313239.~~70000000~~20000000 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 2328,~~869~~864,~~010~~664.1380 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) 0(4,716.0017) Prepayment Penalties ~~309~~431,~~299~~323.4792 Total Deposits 2429,~~178~~291,~~309~~272.6055 Withdrawals Reimbursement for Servicer Advances 0.00 Payment of Service Fee ~~163~~157,~~034~~923.0222 Payment of Interest and Principal 2429,~~015~~133,~~275~~349.5833 Total Withdrawals (Pool Distribution Amount) 2429,~~178~~291,~~309~~272.6055 Ending Balance 0.00

SERVICING FEES Gross Servicing Fee ~~158~~153,~~799~~821.4232 Trustee Fee -Wells Fargo Bank, NA 4,~~234~~101.6090 Supported Prepayment/Curtailment Interest Shortfall 0.00 Net Servicing Fee ~~163~~157,~~034~~923.0222

OTHER ACCOUNTS Beginning Current Current Ending Account Type Balance Withdrawals Deposits Balance Reserve Fund 1,000.00 0.0100 0.01 1,000.0001 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 8 01 0 89 ~~939~~870,~~747~~863.5433 0278,241.0084 0.00 ~~939~~1,~~747~~149,105.5417 30 Days 4858 0 03 0 4861 810,~~522~~268,~~425~~114.4374 0.00 0722,030.0075 0.00 810,~~522~~990,~~425~~145.4349 60 Days 815 10 96 0 1821 12,~~462~~787,~~179~~493.5224 ~~50,043~~0.1400 1640,~~531,410~~012.7353 0.00 3,~~043~~427,~~633~~505.3977 90 Days 67 01 1321 1 2030 1,~~083~~010,~~425~~680.5779 050,043.0014 12,~~494~~874,~~067~~459.4996 91,958.86 24,~~669~~027,~~451~~142.9275 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 6280 9 2231 1 94121 1114,~~068~~066,~~030~~288.5277 ~~989~~920,~~790~~906.6847 34,~~025~~514,~~478~~745.2208 91,958.86 1519,~~175~~593,~~258~~899.2818 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.~~200351~~207361% 0.~~000000~~025920% 0.000000% 0.~~200351~~233281% 0.~~152689~~147484% 0.~~000000~~047121% 0.000000% 0.~~152689~~194606% 30 Days 1.~~202104~~503370% 0.000000% 0.~~000000~~077760% 0.000000% 1.~~202104~~581130% 1.~~384716~~738947% 0.000000% 0.~~000000~~122279% 0.000000% 1.~~384716~~861226% 60 Days 0.~~200351~~388802% 0.~~025044~~000000% 0.~~225394~~155521% 0.000000% 0.~~450789~~544323% 0.~~237574~~472073% 0.~~008131~~000000% 0.~~248822~~108389% 0.000000% 0.~~494527~~580462% 90 Days 0.~~150263~~181441% 0.~~000000~~025920% 0.~~325570~~544323% 0.~~025044~~025920% 0.~~500877~~777605% 0.~~176034~~171163% 0.~~000000~~008475% 0.~~242755~~486802% 0.~~014941~~015574% 0.~~433730~~682013% 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 12.~~552717~~073613% 0.~~225394~~233281% 0.~~550964~~803525% 0.~~025044~~025920% 23.~~354120~~136340% 12.~~798323~~382184% 0.~~160820~~155959% 0.~~491577~~764591% 0.~~014941~~015574% 23.~~465662~~318307%

OTHER INFORMATION Current Period Class A Insufficient Funds 0.00 Principal Balance of Contaminated Properties 0.00 Periodic Advance ~~222~~231,~~261~~628.3623 Class M-1 83,621,854.23 12.30001120% 83,622,396.32 1314.~~59083217~~16731282% 67.~~850643~~141226% 0.000000% Class M-2 49,288,854.23 7.24994040% 49,289,396.32 8.~~01081938~~35061332% 5.~~580013~~816700% 0.000000% Class M-3 38,750,854.23 5.69989682% 38,751,396.32 6.~~29811805~~56526455% 1.~~712701~~785349% 0.000000% Class M-4 30,592,854.23 4.49992951% 30,593,396.32 45.~~97222913~~18313556% 1.~~325889~~382129% 0.000000% Class CE 100.00 0.00001471% 100.00 0.~~00001625~~00001694% 1.~~270678~~324576% 0.000000% Class R-II 100.00 0.00001471% 100.00 0.~~00001625~~00001694% 0.000000% 0.000000% Class P 0.00 0.00000000% 0.00 0.00000000% 0.~~000016~~000017% 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.~~474981~~466104% Weighted Average Net Coupon 7.~~174981~~166104% Weighted Average Pass-Through Rate 7.~~166981~~158104% Weighted Average Maturity(Stepdown Calculation ) ~~348~~347 Beginning Scheduled Collateral Loan Count 43,~~098~~993 Number Of Loans Paid In Full ~~105~~135 Ending Scheduled Collateral Loan Count 3,~~993~~858 Beginning Scheduled Collateral Balance ~~635~~615,~~197~~285,~~596~~328.7218 Ending Scheduled Collateral Balance ~~615~~590,~~285~~248,~~328~~816.1889 Ending Actual Collateral Balance at 3031-~~Jun~~Jul-2004 ~~615~~590,~~463~~478,~~893~~772.4536 Monthly P &I Constant 4,~~495~~349,~~324~~587.3254 Special Servicing Fee 0.00 Prepayment Penalties ~~309~~431,~~299~~323.4792 Realized Loss Amount 04,716.0017 Cumulative Realized Loss 05,207.0023 Ending Scheduled Balance for Premium Loans ~~615~~590,~~285~~248,~~328~~816.1889 Scheduled Principal ~~538~~521,~~582~~433.6899 Unscheduled Principal 1924,~~373~~515,~~685~~077.8630

Miscellaneous Reporting Net Monthly Excess Cashflow 21,~~845~~622,~~294~~602.3204 Extra Principal Ditribution Amount 0.00 OC Amount 7,818,296.32 OC Deficiency Amount 0.00 OC Release Amount 0.00 OC Target Amount 7,818,296.32 Stepdown NO Trigger Event NO Credit Enhancement Percentage 20.441459%

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.~~581210~~571656 9.~~464894~~464943 7.~~529147~~516557 Weighted Average Net Rate 7.~~281210~~271656 9.~~164887~~164965 7.~~229147~~216557 Weighted Average Maturity ~~348~~347 ~~348~~347 ~~348~~347 Beginning Loan Count ~~744~~728 3 1,~~215~~176 Loans Paid In Full 1613 0 3950 Ending Loan Count ~~728~~715 3 1,~~176~~126 Beginning Scheduled Balance ~~100~~97,~~349~~703,~~589~~158.9370 256,~~513~~379.8137 ~~175~~168,~~434~~609,~~113~~291.8369 Ending scheduled Balance 9795,~~703~~778,~~158~~319.7003 256,~~379~~243.3788 ~~168~~160,~~609~~129,~~291~~610.6990 Record Date 0607/3031/2004 0607/3031/2004 0607/3031/2004 Principal And Interest Constant ~~727~~708,~~682~~869.1926 2,157.67 1,~~235~~184,~~267~~877.5423 Scheduled Principal 9392,~~706~~390.0637 ~~134~~135.4449 ~~134~~128,~~543~~742.1381 Unscheduled Principal 21,~~552~~832,~~725~~449.1730 0.00 68,~~690~~350,~~279~~937.0198 Scheduled Interest ~~633~~616,~~976~~478.1389 2,~~023~~022.2318 1,~~100~~056,~~724~~134.4142 Servicing Fees 2524,~~087~~425.4178 64.1309 4342,~~858~~152.5534 Master Servicing Fees 0.00 0.00 0.00 Trustee Fee ~~668~~651.9835 1.71 1,~~169~~124.5305 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 ~~608~~592,~~219~~053.7418 1,~~957~~958.3909 1,~~055~~013,~~696~~982.3310 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.~~273210~~263656 9.~~156894~~156943 7.~~221147~~208557

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.~~573307~~571709 8.~~113989~~114032 7.~~457615~~460081 Weighted Average Net Rate 7.~~273307~~271709 7.~~814001~~814019 7.~~157615~~160080 Weighted Average Maturity ~~348~~347 ~~348~~347 ~~348~~347 Beginning Loan Count ~~392~~387 4 ~~620~~596 Loans Paid In Full 57 0 2423 Ending Loan Count ~~387~~380 4 ~~596~~573 Beginning Scheduled Balance 5453,~~362~~662,~~930~~591.9293 306,~~411~~146.5468 9490,~~480~~364,~~728~~111.1518 Ending scheduled Balance 5352,~~662~~622,~~591~~855.9360 ~~306~~305,~~146~~880.6871 9086,~~364~~304,~~111~~244.1844 Record Date 0607/3031/2004 0607/3031/2004 0607/3031/2004 Principal And Interest Constant ~~392~~387,~~328~~147.4836 2,286.04 ~~660~~632,~~741~~807.9192 Scheduled Principal 4948,~~239~~549.1941 ~~214~~215.1997 7371,~~574~~038.5130 Unscheduled Principal ~~651~~991,~~099~~186.8092 50.6700 43,~~043~~988,~~042~~828.4644 Scheduled Interest ~~343~~338,~~089~~597.2995 2,~~071~~070.8507 ~~587~~561,~~167~~769.4062 Servicing Fees 13,~~590~~415.7264 76.6054 2322,~~620~~591.1904 Master Servicing Fees 0.00 0.00 0.00 Trustee Fee ~~362~~357.4477 2.04 ~~629~~602.8643 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 ~~329~~325,~~136~~182.1333 1,993.2153 ~~562~~539,~~917~~178.3555 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.~~265307~~263709 7.~~805989~~806032 7.~~149615~~152080

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.~~390110~~372005 6.~~699965~~700031 7.~~333211~~325065 Weighted Average Net Rate 7.~~090110~~072006 6.~~399955~~400010 7.~~033211~~025065 Weighted Average Maturity ~~346~~345.00 ~~346~~345.00 ~~346~~345.00 Record Date 0607/3031/2004 0607/3031/2004 0607/3031/2004 Principal And Interest Constant ~~662~~645,~~559~~740.8691 597.83 ~~811~~785,~~702~~103.8032 Beginning Loan Count ~~535~~525 1 ~~584~~573 Loans Paid In Full 1014 0 1128 Ending Loan Count ~~525~~511 1 ~~573~~545 Beginning Scheduled Balance 9290,~~402~~125,~~658~~956.9394 92,~~156~~073.9061 ~~117~~114,~~512~~165,~~492~~618.7108 Ending Scheduled Balance 9087,~~125~~763,~~956~~958.9498 9291,~~073~~989.6186 ~~114~~106,~~165~~995,~~618~~713.0849 Scheduled Principal 9392,~~505~~066.0171 83.2975 9388,~~582~~211.8618 Unscheduled Principal 2,~~183~~269,~~196~~931.9825 0.00 37,~~253~~081,~~291~~693.7741 Scheduled Interest ~~569~~553,~~054~~674.8520 514.5408 ~~718~~696,~~119~~892.9414 Servicing Fee 2322,~~100~~531.6748 23.0402 2928,~~378~~541.1139 Master Servicing Fee 0.00 0.00 0.00 Trustee Fee ~~616~~600.0183 0.61 ~~783~~761.4211 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 ~~545~~531,~~338~~142.1782 490.8945 ~~687~~668,~~958~~350.4185 Realized Loss Amount 0.00 0.00 04,716.0017 Cumulative Realized Loss 0.00 0491.0006 04,716.0017 Percentage of Cumulative Losses 0.0000 0.~~0000~~5314 0.~~0000~~0036 Prepayment Penalties 0.00 0.00 0.00 Special Servicing Fee 0.00 0.00 0.00 Pass-Through Rate 7.~~082110~~064005 6.~~391965~~392031 7.~~025211~~017065

Group Level Collateral Statement Group Total Collateral Description Mixed Fixed & Arm Weighted Average Coupon Rate 7.~~474981~~466104 Weighted Average Net Rate 7.~~174981~~166104 Weighted Average Maturity ~~348~~347.00 Record Date 0607/3031/2004 Principal And Interest Constant 4,~~495~~349,~~324~~587.3254 Beginning Loan Count 43,~~098~~993 Loans Paid In Full ~~105~~135 Ending Loan Count 3,~~993~~858 Beginning Scheduled Balance ~~635~~615,~~197~~285,~~596~~328.7218 Ending Scheduled Balance ~~615~~590,~~285~~248,~~328~~816.1889 Scheduled Principal ~~538~~521,~~582~~433.6899 Unscheduled Principal 1924,~~373~~515,~~685~~077.8630 Scheduled Interest 3,~~956~~828,~~741~~153.6455 Servicing Fee ~~158~~153,~~799~~821.4232 Master Servicing Fee 0.00 Trustee Fee 4,~~234~~101.6090 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,~~793~~674,~~707~~331.6290 Realized Loss Amount 04,716.0017 Cumulative Realized Loss 05,207.0023 Percentage of Cumulative Losses 0.~~0000~~0008 Prepayment Penalties 0.00 Special Servicing Fee 0.00 Pass-Through Rate 7.~~166981~~158104

Filing Compare · MASTR ASSET BACKED SECURITIES TRUST 2004-OPT1