Fitch Rates Washington Mutual MSC Mtge P-T Ctfs $335.9MM Series 2004-RA3

Business Wire, July 30, 2004

NEW YORK -- Washington Mutual Mortgage Securities Corp.'s mortgage pass-through certificates, series 2004-RA3 is rated by Fitch Ratings as follows:

-- $335,926,100 classes I-A, II-A, and R (senior certificates) 'AAA'.

The classes C-B-1 through C-B-6 certificates are not rated by Fitch.

The 'AAA' rating on the senior certificates reflects the 2.40% subordination provided by the class C-B certificates (which are not rated by Fitch). 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. The ratings also reflect the quality of the mortgage collateral, the capabilities of Washington Mutual Mortgage Securities Corp. (WMMSC) as master servicer (rated 'RMS2+' by Fitch), and Fitch's confidence in the integrity of the legal and financial structure of the transaction.

Of mortgage loans deposited into the Washington Mutual MSC mortgage pass-through certificates series 2004-RA3 trust, 90.2% were seasoned loans originated by Washington Mutual Bank, FA, Washington Mutual Bank fsb, Washington Mutual Bank, or an affiliate, and subsequently purchased by WMMSC. The remaining 9.8% were purchased by WMMSC through its optional termination rights of various trusts.

The assets of the trust will consist of two groups of 15- and 30-year fixed-rate loans, secured by first liens on one- to four-family properties, with a total of 2,579 loans. As of July 1, 2004 (the cutoff date), the total original principal balance is $344,186,917. The two loan groups are cross-collateralized.

The Group I loans consist of 879 conventional, fully amortizing, 15-year fixed-rate mortgage loans with an aggregate original principal balance of $83,534,100.88. The average unpaid principal balance is $95,033. The weighted average loan-to-value ratio (LTV) is 46.6%. Rate/Term and Cash-out refinance loans represent 35.07% and 36.94% of the loan pool, respectively. Second home and investor-occupied loans comprise 5.55% and 5.19% of the group, respectively. The weighted average FICO credit score for the group is 734. The weighted average remaining term for the group is 112.8 months. The states that represent the largest portion of the mortgage loans are Texas (24.98%), Washington (23.47%), Oregon (12.01%), New York (6.50%), and California (5.40%). All other states represent less than 5% of the outstanding balance of the pool.

The Group II loans consist of 1,700 conventional, fully amortizing, 30-year fixed-rate mortgage loans with an aggregate original principal balance of $260,652,817.06. The average unpaid principal balance is $153,325. The weighted average LTV is 65.6%. Rate/Term and Cash-out refinance loans represent 30.25% and 18.95% of the loan pool, respectively. Second home and investor-occupied loans comprise 3.47% and 3.94% of the group, respectively. The weighted average FICO credit score for the group is 721. The weighted average remaining term for the group is 286.3 months. The states that represent the largest portion of the mortgage loans are Washington (29.12%), California (15.73%), Oregon (12.93%), Texas (6.83%), and New York (6.43%). All other states represent less than 5% of the outstanding balance of the pool.

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', available on the Fitch Ratings web site at 'www.fitchratings.com'.

The certificates are issued pursuant to a pooling and servicing agreement dated July 1, 2004 among Washington Mutual Mortgage Securities Corp., as depositor and master servicer and U.S. Bank National Associate, as trustee. For federal income tax purposes, elections will be made to treat the trust as two separate real estate mortgage investment conduits (REMICs).