Prostaglandin (PG) E2 formation, especially relevant for renal function in the state of renal vascular disease, is inhibited by omega-3 fatty acids. On the other hand, omega-3 fatty acids are under evaluation in chronic inflammatory kidney diseases, because of their ability to modulate immunologic cell response. We evaluated the effect of 1.7 g/d eicosapentaenoic acid (EPA), given with cod liver oil for four weeks to elderly persons with atherosclerosis. Enrichment of EPA coincided with inhibition of PG biosynthesis, transiently plasma creatinine increased, while creatinine clearance and excretion of solutes with the urine decreased in our experimental subjects. At the end of the four week study no effect of omega-3 fatty acids on renal function was found. Further studies are warranted to evaluate the potential benefit of omega-3 fatty acids on renal function in elderly persons.