We have previously generated a mouse transgenic line with an insertional mutation designated lpd that demonstrates a phenotype of hypertriglyceridemia and fatty liver. Since the recently identified phosphatidylserine-specific phospholipase A1 (PS-PLA1) demonstrates significant homology to triglyceride lipases, we reasoned that the mouse Ps-plaI gene may be the disrupted gene within the lpd locus. Using a rat PS-PLA1 cDNA sequence to search the EST database, we identified a mouse EST homolog AA839424. Sequencing analysis of AA839424 revealed a putative Ps-pla1 protein of 456 amino acids with extensive overall structural conservation with human and rat PS-PLA1 and with triglyceride lipases. Conserved sequences in Ps-pla1 include a lipase consensus sequences GxSxG, a catalytic triad, and eight of the ten conserved cysteine residues that are required for tertiary structure. Mouse Ps-plal carries a phosphatidylserine-binding motif that is absent in all triglyceride lipases. Using a mouse whole-genome radiation hybrid (WG-RH) mapping panel (T31), we mapped mouse Ps-pla1 to Chromosome (Chr) 16 between genetic markers D16Mit194 and D16Mit38, which is 17.1 cM centromeric to the lpd locus. On the basis of chromosome location, we conclude that Ps-pla1 and lpd are distinct genes in lipid metabolism.