The effect of consuming eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) on platelet-activating factor (PAF) biosynthesis by renal acetyl-CoA: 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) acetyltransferase activity was compared in rats fed diets containing fish oil (FO) or sunflower oil (SO) for 11 months. Microsomes from the FO group exhibited a significantly lower formation of [14C]PAF from [1-14C]acetyl-CoA in the absence of exogenously-added lysoPAF. There were no differences between the two groups in the generation of radioactive acylacetyl-glycerophosphocholine (GPC) upon incubation of microsomes without added lysoPAF. Upon addition of lysoPAF, the microsomal synthesis of PAF, but not acylacetyl-GPC, rose considerably. Furthermore, PAF synthesis via microsomal acetyltransferase activity in the FO-fed animals was only 40% that of the SO groups. These findings may bear potential relevance in terms of reducing PAF synthesis in association with renal pathophysiology.