Moody’s Investors Service said late Wednesday that the serious delinquency rate (60 days or more past due) on securitized prime jumbo mortgage pools fell slightly during March 2007, the first month over the last nine in which the delinquency rate declined from the prior period. From the press release:

Moody’s 60+ day delinquency rate index was 0.378% in March 2007 compared with 0.383% in February 2007 and 0.278% a year ago in March 2006. Serious delinquencies over the first quarter of 2007 measured 0.370% compared to 0.329% in the fourth quarter of 2006. Serious delinquencies continue to remain relatively low in absolute terms.

A full report on Jumbo index performance is available to paid subscribers of Moody’s services. Also: Moody’s noted that it, like Fitch, is altering the way it rates subprime RMBS deals. I’ve made a copy of the press statement on this available here.