The effect of fatty fish consumption on plasma lipid and lipoprotein concentrations was studied in 118 healthy men in a cross-over controlled trial. Subjects ate 100 g or more of fatty fish at least twice a week for 3 months, and little or no fatty fish for another 3 months. The mean plasma triglyceride concentration decreased significantly by 6.7% on the fish diet; there were no significant changes in plasma total cholesterol, high-density lipoprotein cholesterol, or low-density lipoprotein cholesterol. A realistic intake of fatty fish has a detectable effect on blood lipids.