8-K 1 mab03op1.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 25, 2003 MASTR ASSET BACKED SECURITIES TRUST Mortgage Pass-Through Certificates, Series 2003-OP1 Trust (Exact name of registrant as specified in its charter) New York (governing law of 333-75724-15 54-2102389 Pooling and Servicing Agreement) (Commission 54-2102390 (State or other File Number) IRS EIN jurisdiction of Incorporation) c/o Wells Fargo Bank Minnesota, 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) ITEM 5. Other Events On September 25, 2003 a distribution was made to holders of MASTR ASSET BACKED SECURITIES TRUST, Mortgage Pass-Through Certificates, Series 2003-OP1 Trust. ITEM 7. Financial Statements and Exhibits (c) Exhibits furnished in accordance with Item 601(a) of Regulation S-K Exhibit Number Description EX-99.1 Monthly report distributed to holders of Mortgage Pass-Through Certificates, Series 2003-OP1 Trust, relating to the September 25, 2003 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 2003-OP1 Trust By: Wells Fargo Bank Minnesota, N.A., as Trustee By: /s/ Beth Belfield, Assistant Vice President By: Beth Belfield, Assistant Vice President Date: 10/6/03 INDEX TO EXHIBITS Exhibit Number Description EX-99.1 Monthly report distributed to holders of Mortgage Pass-Through Certificates, Series 2003-OP1 Trust, relating to the September 25, 2003 distribution. EX-99.1

MASTR Asset Backed Securitizations Mortgage Pass-Through Certificates Record Date: 78/31/03 Distribution Date: 89/25/03 MABS Series: 2003-OP1 Contact: Customer Service - CTSLink Wells Fargo Bank Minnesota, 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 57643LAQ9 SEN 2.~~10000~~11000% ~~860~~830,~~118~~375,~~864~~022.8285 1,~~555~~508,~~381~~745.6128 2932,~~743~~817,~~841~~150.9860 A-2 57643LAJ5 SEN 1.~~52000~~53000% ~~322~~312,~~992~~714,~~728~~140.5068 ~~422~~412,~~761~~000.5988 109,~~278~~835,~~587~~325.8210 M-1 57643LAK2 MEZ 1.~~95000~~96000% 58,600,000.00 98,~~399~~903.1778 0.00 M-2 57643LAL0 MEZ 2.~~95000~~96000% 51,275,000.00 130,~~252~~694.7428 0.00 M-3 57643LAM8 MEZ 3.~~85000~~86000% 21,975,000.00 7273,~~853~~042.2346 0.00 M-4 57643LAN6 MEZ 5.~~00000~~01000% 18,313,000.00 7879,~~847~~005.6433 0.00 MV-5 57643LAP1 MEZ 4.~~60000~~61000% 4,650,000.00 18,~~419~~459.1721 0.00 MF-5 57643LAR7 MEZ 6.00000% 10,000,000.00 50,000.00 0.00 CE MAB03OP1C OC 0.00000% 10,980,010.85 5,~~228~~051,~~066~~282.6894 0.00 R-I MAB03OPR1 RES 0.00000% 0.00 0.00 0.00 R-II MAB03OPR2 RES 0.00000% 0.00 0.00 0.00 P MAB03OPTP Pre_Pay 0.00000% 100.00 ~~895~~847,~~544~~776.3079 0.00 Totals 1,~~358~~318,~~904~~882,~~704~~274.1738 8,~~550~~269,~~526~~910.1395 4042,~~022~~652,~~429~~475.8070

Certificateholder Distribution Summary (continued) Current Ending Cumulative Realized Certificate Total Realized Class Loss Balance Distribution Losses A-1 0.00 ~~830~~797,~~375~~557,~~022~~872.8525 3134,~~299~~325,~~223~~895.5988 0.00 A-2 0.00 ~~312~~302,~~714~~878,~~140~~815.6858 10,~~701~~247,~~349~~325.4198 0.00 M-1 0.00 58,600,000.00 98,~~399~~903.1778 0.00 M-2 0.00 51,275,000.00 130,~~252~~694.7428 0.00 M-3 0.00 21,975,000.00 7273,~~853~~042.2346 0.00 M-4 0.00 18,313,000.00 7879,~~847~~005.6433 0.00 MV-5 0.00 4,650,000.00 18,~~419~~459.1721 0.00 MF-5 0.00 10,000,000.00 50,000.00 0.00 CE 0.00 10,980,010.85 5,~~228~~051,~~066~~282.6894 0.00 R-I 0.00 0.00 0.00 0.00 R-II 0.00 0.00 0.00 0.00 P 0.00 100.00 ~~895~~847,~~544~~776.3079 0.00 Totals 0.00 1,~~318~~276,~~882~~229,~~274~~798.3868 4850,~~572~~922,~~955~~386.9365 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-1 939,100,000.00 ~~860~~830,~~118~~375,~~864~~022.8285 0.00 2932,~~743~~817,~~841~~150.9860 0.00 0.00 A-2 349,107,000.00 ~~322~~312,~~992~~714,~~728~~140.5068 0.00 109,~~278~~835,~~587~~325.8210 0.00 0.00 M-1 58,600,000.00 58,600,000.00 0.00 0.00 0.00 0.00 M-2 51,275,000.00 51,275,000.00 0.00 0.00 0.00 0.00 M-3 21,975,000.00 21,975,000.00 0.00 0.00 0.00 0.00 M-4 18,313,000.00 18,313,000.00 0.00 0.00 0.00 0.00 MV-5 4,650,000.00 4,650,000.00 0.00 0.00 0.00 0.00 MF-5 10,000,000.00 10,000,000.00 0.00 0.00 0.00 0.00 CE 10,981,347.20 10,980,010.85 0.00 0.00 0.00 0.00 R-I 0.00 0.00 0.00 0.00 0.00 0.00 R-II 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 1,464,001,447.20 1,~~358~~318,~~904~~882,~~704~~274.1738 0.00 4042,~~022~~652,~~429~~475.8070 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 2932,~~743~~817,~~841~~150.9860 ~~830~~797,~~375~~557,~~022~~872.8525 0.~~88422428~~84927896 2932,~~743~~817,~~841~~150.9860 A-2 109,~~278~~835,~~587~~325.8210 ~~312~~302,~~714~~878,~~140~~815.6858 0.~~89575443~~86758162 109,~~278~~835,~~587~~325.8210 M-1 0.00 58,600,000.00 1.00000000 0.00 M-2 0.00 51,275,000.00 1.00000000 0.00 M-3 0.00 21,975,000.00 1.00000000 0.00 M-4 0.00 18,313,000.00 1.00000000 0.00 MV-5 0.00 4,650,000.00 1.00000000 0.00 MF-5 0.00 10,000,000.00 1.00000000 0.00 CE 0.00 10,980,010.85 0.99987831 0.00 R-I 0.00 0.00 0.00000000 0.00 R-II 0.00 0.00 0.00000000 0.00 P 0.00 100.00 1.00000000 0.00 Totals 4042,~~022~~652,~~429~~475.8070 1,~~318~~276,~~882~~229,~~274~~798.3868 0.~~90087498~~87174080 4042,~~022~~652,~~429~~475.8070

Principal Distribution Factors Statement Original Beginning Scheduled Unscheduled Face Certificate Principal Principal Class (2) Amount Balance Distribution Distribution Accretion A-1 939,100,000.00 ~~915~~884.~~89699161~~22428160 0.00000000 3134.~~67271002~~94532063 0.00000000 A-2 349,107,000.00 ~~925~~895.~~19694105~~75442681 0.00000000 2928.~~44251424~~17280977 0.00000000 M-1 58,600,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-2 51,275,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-3 21,975,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 M-4 18,313,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 MV-5 4,650,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 MF-5 10,000,000.00 1000.00000000 0.00000000 0.00000000 0.00000000 CE 10,981,347.20 999.87830728 0.00000000 0.00000000 0.00000000 R-I 0.00 0.00000000 0.00000000 0.00000000 0.00000000 R-II 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 $1000 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 3134.~~67271002~~94532063 ~~884~~849.~~22428160~~27896097 0.~~88422428~~84927896 3134.~~67271002~~94532063 A-2 0.00000000 2928.~~44251424~~17280977 ~~895~~867.~~75442681~~58161704 0.~~89575443~~86758162 2928.~~44251424~~17280977 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 MV-5 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 MF-5 0.00000000 0.00000000 1,000.00000000 1.00000000 0.00000000 CE 0.00000000 0.00000000 999.87830728 0.99987831 0.00000000 R-I 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 R-II 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, Bankrupcy, 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-1 939,100,000.00 2.~~10000~~11000% ~~860~~830,~~118~~375,~~864~~022.8285 1,~~555~~508,~~381~~745.6128 0.00 0.00 A-2 349,107,000.00 1.~~52000~~53000% ~~322~~312,~~992~~714,~~728~~140.5068 ~~422~~412,~~761~~000.5988 0.00 0.00 M-1 58,600,000.00 1.~~95000~~96000% 58,600,000.00 98,~~399~~903.1778 0.00 0.00 M-2 51,275,000.00 2.~~95000~~96000% 51,275,000.00 130,~~252~~694.7428 0.00 0.00 M-3 21,975,000.00 3.~~85000~~86000% 21,975,000.00 7273,~~853~~042.2346 0.00 0.00 M-4 18,313,000.00 5.~~00000~~01000% 18,313,000.00 7879,~~847~~005.6433 0.00 0.00 MV-5 4,650,000.00 4.~~60000~~61000% 4,650,000.00 18,~~419~~459.1721 0.00 0.00 MF-5 10,000,000.00 6.00000% 10,000,000.00 50,000.00 0.00 0.00 CE 10,981,347.20 0.00000% 10,980,010.85 0.00 0.00 0.00 R-I 0.00 0.00000% 0.00 0.00 0.00 0.00 R-II 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 1,464,001,447.20 2,~~426~~370,~~915~~851.1522 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 1,~~555~~508,~~381~~745.6128 0.00 ~~830~~797,~~375~~557,~~022~~872.8525 A-2 0.00 0.00 ~~422~~412,~~761~~000.5988 0.00 ~~312~~302,~~714~~878,~~140~~815.6858 M-1 0.00 0.00 98,~~399~~903.1778 0.00 58,600,000.00 M-2 0.00 0.00 130,~~252~~694.7428 0.00 51,275,000.00 M-3 0.00 0.00 7273,~~853~~042.2346 0.00 21,975,000.00 M-4 0.00 0.00 7879,~~847~~005.6433 0.00 18,313,000.00 MV-5 0.00 0.00 18,~~419~~459.1721 0.00 4,650,000.00 MF-5 0.00 0.00 50,000.00 0.00 10,000,000.00 CE 0.00 0.00 5,~~228~~051,~~066~~282.6894 0.00 10,980,010.85 R-I 0.00 0.00 0.00 0.00 0.00 R-II 0.00 0.00 0.00 0.00 0.00 P 0.00 0.00 ~~895~~847,~~544~~776.3079 0.00 100.00 Totals 0.00 0.00 8,~~550~~269,~~526~~910.1395 0.00 (4) Amount Does Not Include Excess Special Hazard, Bankrupcy, 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-1 939,100,000.00 2.~~10000~~11000% ~~915~~884.~~89699161~~22428160 1.~~65624706~~60658639 0.00000000 0.00000000 A-2 349,107,000.00 1.~~52000~~53000% ~~925~~895.~~19694105~~75442681 1.~~21097999~~18015646 0.00000000 0.00000000 M-1 58,600,000.00 1.~~95000~~96000% 1000.00000000 1.~~67916672~~68777782 0.00000000 0.00000000 M-2 51,275,000.00 2.~~95000~~96000% 1000.00000000 2.~~54027772~~54888893 0.00000000 0.00000000 M-3 21,975,000.00 3.~~85000~~86000% 1000.00000000 3.~~31527782~~32388896 0.00000000 0.00000000 M-4 18,313,000.00 5.~~00000~~01000% 1000.00000000 4.~~30555562~~31416644 0.00000000 0.00000000 MV-5 4,650,000.00 4.~~60000~~61000% 1000.00000000 3.~~96111183~~96972258 0.00000000 0.00000000 MF-5 10,000,000.00 6.00000% 1000.00000000 5.00000000 0.00000000 0.00000000 CE 10,981,347.20 0.00000% 999.87830728 0.00000000 0.00000000 0.00000000 R-I 0.00 0.00000% 0.00000000 0.00000000 0.00000000 0.00000000 R-II 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 $1000 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.~~65624706~~60658639 0.00000000 ~~884~~849.~~22428160~~27896097 A-2 0.00000000 0.00000000 1.~~21097999~~18015646 0.00000000 ~~895~~867.~~75442681~~58161704 M-1 0.00000000 0.00000000 1.~~67916672~~68777782 0.00000000 1000.00000000 M-2 0.00000000 0.00000000 2.~~54027772~~54888893 0.00000000 1000.00000000 M-3 0.00000000 0.00000000 3.~~31527782~~32388896 0.00000000 1000.00000000 M-4 0.00000000 0.00000000 4.~~30555562~~31416644 0.00000000 1000.00000000 MV-5 0.00000000 0.00000000 3.~~96111183~~96972258 0.00000000 1000.00000000 MF-5 0.00000000 0.00000000 5.00000000 0.00000000 1000.00000000 CE 0.00000000 0.00000000 ~~476~~459.~~08609261~~98754506 0.00000000 999.87830728 R-I 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 R-II 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 P 0.00000000 0.00000000 ~~8955443~~8477767.~~00000000~~90000000 0.00000000 1000.00000000 (6) Amount Does Not Include Excess Special Hazard, Bankrupcy,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 4951,~~184~~528,~~164~~544.2520 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) (4535,~~051~~601.7949) Prepayment Penalties ~~895~~847,~~544~~776.3079 Total Deposits 5052,~~034~~340,~~656~~719.7650 Withdrawals Reimbursement for Servicer Advances 0.00 Payment of Service Fee 1,~~461~~418,~~700~~332.8385 Payment of Interest and Principal 4850,~~572~~922,~~955~~386.9365 Total Withdrawals (Pool Distribution Amount) 5052,~~034~~340,~~656~~719.7650 Ending Balance 0.00

SERVICING FEES Gross Servicing Fee ~~566~~549,~~210~~534.2483 Radian ~~892~~865,~~093~~499.2451 Trustee Fee - Wells Fargo 3,~~397~~298.3551 Supported Prepayment/Curtailment Interest Shortfall 0.00 Net Servicing Fee 1,~~461~~418,~~700~~332.8385

OTHER ACCOUNTS Beginning Current Current Ending Account Type Balance Withdrawals Deposits Balance Reserve Fund 1,000.00 0.0001 0.0001 1,000.00 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 2638 13 0 2741 34,~~380~~550,~~348~~540.5390 ~~164~~521,~~288~~062.1321 0.00 35,~~544~~071,~~636~~603.6611 30 Days ~~141~~140 01 5 0 146 19,~~034~~305,~~427~~862.5642 065,231.0096 ~~645~~919,~~076~~709.1670 0.00 1920,~~679~~290,~~503~~804.7208 60 Days 2324 72 4436 0 7462 2,~~976~~856,~~108~~961.7937 ~~860~~144,~~684~~489.7939 74,~~088~~673,~~713~~712.1551 0.00 107,~~925~~675,~~506~~163.7327 90 Days 1013 1934 ~~127~~154 35 ~~159~~206 1,~~333~~782,~~951~~410.9011 24,~~213~~203,~~759~~330.3904 1823,~~666~~190,~~834~~717.1225 ~~187~~323,~~973~~375.0794 2229,~~402~~499,~~518~~833.4834 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 ~~174~~177 5275 ~~177~~198 35 ~~406~~455 23,~~344~~945,~~488~~233.2590 68,~~454~~963,~~792~~592.7129 2629,~~564~~305,~~911~~201.5667 ~~187~~323,~~973~~375.0794 5662,~~552~~537,~~165~~403.5980 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.~~288793~~433839% 0.~~011107~~034250% 0.000000% 0.~~299900~~468090% 0.~~256220~~356428% 0.~~012453~~040813% 0.000000% 0.~~268673~~397241% 30 Days 1.~~566145~~598356% 0.~~000000~~011417% 0.~~055537~~057084% 0.000000% 1.~~621682~~666857% 1.~~442751~~512162% 0.~~000000~~005109% 0.~~048895~~072038% 0.000000% 1.~~491646~~589309% 60 Days 0.~~255470~~274004% 0.~~077752~~022834% 0.~~488726~~411006% 0.000000% 0.~~821948~~707843% 0.~~225580~~223776% 0.~~065237~~011317% 0.~~537303~~366076% 0.000000% 0.~~828120~~601169% 90 Days 0.~~111074~~148419% 0.~~211041~~388172% 1.~~410641~~758192% 0.~~033322~~057084% 12.~~766078~~351867% 0.~~101109~~139610% 0.~~167796~~329232% 1.~~414889~~816449% 0.~~014248~~025329% 12.~~698042~~310621% 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.~~932689~~020779% 0.~~577585~~856262% 12.~~966011~~260532% 0.~~033322~~057084% 45.~~509608~~194657% 1.~~769441~~875548% 0.~~489254~~702087% 2.~~013539~~295376% 0.~~014248~~025329% 4.~~286481~~898340%

OTHER INFORMATION Current Period Class A Insufficient Funds 0.00 Principal Balance of Contaminated Properties 0.00 Periodic Advance ~~656~~752,~~998~~365.30 Class A-1 524,901,347.20 35.85388172% 478,671,826.43 37.50671132% 62.493281% 0.000000% Class A-2 175,794,347.20 12.00779873% 175,793,010.85 13.77440105% 23.732310% 0.000000% Class M-1 117,194,347.20 8.00507045% 117,193,010.85 9.18275149% 4.591650% 0.000000% Class M-2 65,919,347.20 4.50268320% 65,918,010.85 5.16505812% 4.017693% 0.000000% Class M-3 43,944,347.20 3.00166009% 43,943,010.85 3.44318953% 1.721869% 0.000000% Class M-4 25,631,347.20 1.75077335% 25,630,010.85 2.00825987% 1.434930% 0.000000% Class CE 0.00 0.00000000% 0.00 0.00000000% 0.860347% 0.000000% Class R-I 0.00 0.00000000% 0.00 0.00000000% 0.000000% 0.000000% Class R-II 0.00 0.00000000% 0.00 0.00000000% 0.000000% 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 8.~~074639~~075736% Weighted Average Net Coupon 7.~~574639~~575736% Weighted Average Pass-Through Rate 6.~~783864~~785250% Weighted Average Maturity(Stepdown Calculation ) ~~348~~347 Beginning Scheduled Collateral Loan Count 9,~~238~~003 Number Of Loans Paid In Full ~~235~~244 Ending Scheduled Collateral Loan Count 98,~~003~~759 Beginning Scheduled Collateral Balance 1,~~358~~318,~~904~~882,~~704~~274.1838 Ending Scheduled Collateral Balance 1,~~318~~276,~~882~~229,~~274~~798.3868 Ending Actual Collateral Balance at 31-~~Jul~~Aug-2003 1,~~319~~276,~~314~~706,~~566~~079.8769 Monthly P &I Constant 109,~~183~~890,~~816~~403.3228 Special Servicing Fee 0.00 Prepayment Penalties ~~895~~847,~~544~~776.3079 Realized Loss Amount 4535,~~051~~601.7949 Cumulative Realized Loss 5792,~~088~~690.9645 Ending Scheduled Balance for Premium Loans 1,~~318~~276,~~882~~229,~~274~~798.3868 Scheduled Principal 1,~~039~~014,~~928~~615.4570 Unscheduled Principal 3841,~~982~~637,~~501~~860.3500

Other Income ~~17,846~~279.5122

Miscellaneous Reporting Net Monthly Excess Cashflow 5,~~273~~086,~~118~~884.4743 Extra Prinicpal Distribution Amount 4535,~~051~~601.7949 OC Amount 10,980,010.85 OC Deficiency Amount 4535,~~051~~601.7949 OC Release Amount 0.00 OC Target Amount 10,980,010.85 Stepdown NO Trigger Event NO Credit Enhancement Percentage 13.~~328939~~774401%

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.~~662821~~664521 8.~~261905~~263659 7.~~621297~~623106 Weighted Average Net Rate 7.~~162822~~164521 7.~~761905~~763659 7.~~121297~~123106 Weighted Average Maturity ~~348~~347 ~~348~~347 ~~339~~338 Beginning Loan Count ~~790~~761 6,~~406~~248 1,~~420~~390 Loans Paid In Full 2918 ~~158~~178 3031 Ending Loan Count ~~761~~743 6,~~248~~070 1,~~390~~359 Beginning Scheduled Balance ~~100~~95,~~046~~788,~~023~~514.6063 ~~888~~863,~~992~~494,~~049~~146.6137 ~~199~~194,~~336~~444,~~906~~712.2134 Ending scheduled Balance 9593,~~788~~356,~~514~~316.6360 ~~863~~833,~~494~~100,~~146~~984.3738 ~~194~~189,~~444~~515,~~712~~563.3456 Record Date 0708/31/2003 0708/31/2003 0708/31/2003 Principal And Interest Constant ~~741~~712,~~163~~436.2251 6,~~726~~535,~~328~~601.2628 1,~~472~~437,~~214~~006.1936 Scheduled Principal ~~102~~100,~~300~~625.9057 ~~605~~589,~~688~~250.6900 ~~206~~201,~~209~~779.3315 Unscheduled Principal 42,~~155~~331,~~208~~572.0746 2429,~~892~~803,~~214~~911.5599 4,~~685~~727,~~984~~369.5463 Scheduled Interest ~~638~~611,~~862~~810.3294 65,~~120~~946,~~639~~351.5728 1,~~266~~235,~~004~~227.8621 Servicing Fees 4139,~~685~~911.8193 ~~370~~359,~~413~~789.3365 8381,~~057~~018.0366 Master Servicing Fees 0.00 0.00 0.00 Trustee Fee ~~250~~239.1661 2,~~222~~159.5187 ~~498~~486.3523 FRY Amount 0.00 0.00 0.00 Special Hazard Fee 0.00 0.00 0.00 Other Fee 7673,~~262~~000.8639 ~~552~~536,~~790~~330.2089 ~~150~~146,~~560~~799.7691 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 ~~597~~571,~~176~~899.5001 5,~~750~~586,~~226~~561.1163 1,~~182~~154,~~947~~208.7555 Realized Loss Amount 0.00 4535,~~051~~601.7949 0.00 Cumulative Realized Loss 0.00 4580,~~051~~653.7928 0.00 Percentage of Cumulative Losses 0.00 0.00 0.00 Prepayment Penalties 0.00 0.00 0.00 Special Servicing Fee 0.00 0.00 0.00 Pass-Through Rate 6.~~245088~~247000 7.~~012724~~015317 6.~~211928~~214141

Group Level Collateral Statement Group Group 4 Total Collateral Description Fixed 15/30 & ARM Mixed Fixed & Arm Weighted Average Coupon Rate 7.~~869932~~864603 8.~~074639~~075736 Weighted Average Net Rate 7.~~369932~~364603 7.~~574639~~575736 Weighted Average Maturity ~~339~~338 ~~348~~347 Beginning Loan Count ~~622~~604 9,~~238~~003 Loans Paid In Full 1817 ~~235~~244 Ending Loan Count ~~604~~587 98,~~003~~759 Beginning Scheduled Balance ~~170~~165,~~529~~154,~~724~~901.7604 1,~~358~~318,~~904~~882,~~704~~274.1838 Ending scheduled Balance ~~165~~160,~~154~~256,~~901~~934.0414 1,~~318~~276,~~882~~229,~~274~~798.3868 Record Date 0708/31/2003 0708/31/2003 Principal And Interest Constant 1,~~244~~205,~~110~~359.6513 109,~~183~~890,~~816~~403.3228 Scheduled Principal ~~125~~122,~~729~~960.5398 1,~~039~~014,~~928~~615.4570 Unscheduled Principal 54,~~249~~775,~~094~~005.1992 3841,~~982~~637,~~501~~860.3500 Scheduled Interest 1,~~118~~082,~~381~~398.1215 98,~~143~~875,~~887~~787.8758 Servicing Fees 7168,~~054~~814.0759 ~~566~~549,~~210~~534.2483 Master Servicing Fees 0.00 0.00 Trustee Fee ~~426~~412.3380 3,~~397~~298.3551 FRY Amount 0.00 0.00 Special Hazard Fee 0.00 0.00 Other Fee ~~112~~109,~~479~~368.4232 ~~892~~865,~~093~~499.2451 Pool Insurance Fee 0.00 0.00 Spread Fee 1 0.00 0.00 Spread Fee 2 0.00 0.00 Spread Fee 3 0.00 0.00 Net Interest 1,~~047~~013,~~327~~583.1056 8,~~577~~326,~~677~~252.4675 Realized Loss Amount 0.00 4535,~~051~~601.7949 Cumulative Realized Loss 12,037.17 5792,~~088~~690.9645 Percentage of Cumulative Losses 0.00 0.00 Prepayment Penalties 0.00 0.00 Special Servicing Fee 0.00 0.00 Pass-Through Rate 6.~~575426~~566944 6.~~783864~~785250

Filing Compare · MORTGAGE ASSET SECURITIZATION TRANSACTIONS INC SER 2003-OPT1