Fitch Rates MASTR Adjustable-Rate Mortgage Trust $566.4MM Series 2004-15

Business Wire, Nov 30, 2004

NEW YORK -- MASTR adjustable-rate mortgage trust 2004-15 $566.4 million mortgage pass-through certificates are rated as follows by Fitch Ratings:

-- $537.9 million classes 1-A-1, 2-A-1, 2-A-2, 3-A-1, 4-A-1, 5-A-1, 6-A-1, 6-A-X, 7-A-1, 8-A-1, 9-A-1, A-LR and A-UR (senior certificates) 'AAA';

-- $12,245,000 class B-1 'AA';

-- $6,835,000 class B-2 'A';

-- $4,271,000 class B-3 'BBB';

-- $2,848,000 privately offered class B-4 'BB';

-- $2,278,000 privately offered class B-5 'B'.

The 'AAA' rating on the senior certificates reflects the 5.55% subordination provided by the 2.15% class B-1, the 1.20% class B-2, the 0.75% class B-3, the 0.50% privately offered class B-4, the 0.40% privately offered class B-5 and the 0.55% privately offered class B-6 certificates. The ratings on the class B certificates reflect their respective subordination.

Fitch believes the above credit enhancement will be adequate to support mortgagor defaults as well as bankruptcy, fraud and special hazard losses in limited amounts. In addition, the ratings also reflect the quality of the underlying mortgage collateral, strength of the legal and financial structures and the master servicing capabilities of Wells Fargo Bank Minnesota, N.A. (rated 'RMS1' by Fitch).

The mortgage loans are separated into nine cross-collateralized mortgage loan groups. Each group's senior certificates will receive interest and/or principal from its respective mortgage loan group. In certain very limited circumstances when a pool experiences either rapid prepayments or disproportionately high realized losses, principal and interest collected from the other loan groups may be applied to pay principal or interest, or both, to the other group's senior certificates. The subordinate certificates will support all five groups and will receive interest and principal from available funds collected in the aggregate from all the mortgage pools.

The nine groups in aggregate contain 2,419 conventional, fully amortizing 30-year short-term, 2/1, 3/1, 5/1, and 7/1 hybrid adjustable-rate mortgage (ARM) loans secured by first liens on one- to four-family residential properties with an aggregate scheduled principal balance of $569,546,232. The average unpaid principal balance of the aggregate pool as of the cut-off date (Nov. 1, 2004) is $235,933. The weighted average original loan-to-value ratio (OLTV) is 75.24%. The weighted average credit score of the borrowers is 722. Approximately 58.67% of the pool was originated under a reduced (non Full/Alternative) documentation program. Second home and investor-occupied properties constitute 5.22% and 11.33% of the loans, respectively. The weighted average mortgage interest rate is 5.149% and the weighted average remaining term to maturity (WAM) is 357 months. The states that represent the largest portion of the aggregate mortgage loans are California (28.95%), Virginia (8.34%), Arizona (6.29%), and Florida (5.42%). All other states represent less than 5% of the aggregate pool balance as of the cut-off date.

None of the mortgage loans are 'high cost' loans as defined under any local, state or federal laws. For additional information on Fitch's rating criteria regarding predatory lending legislation, please see the press release issued May 1, 2003 entitled 'Fitch Revises Rating Criteria in Wake of Predatory Lending Legislation.'

MASTR, a special purpose corporation, deposited the loans into the trust, which issued the certificates. JPMorgan Chase Bank N.A. will act as trustee. For federal income tax purposes, elections will be made to treat the trust fund as multiple real estate mortgage investment conduits (REMICs).