Effects of fish-oil ingestion on cardiovascular risk factors in hyperlipidemic subjects in Israel: a randomized, double-blind crossover study. Effects of a daily fish-oil supplement on serum lipids, apolipoproteins, and some platelet functions and hemorheologic variables were examined in 27 hyperlipidemic subjects in a randomized, controlled, double-blind, crossover fashion with an identically encapsulated vegetable oil serving as the control treatment. Despite the habitual high linoleic acid intake of the study population, significant incorporation of n-3 (omega-3) fatty acids into the serum, platelet, and erythrocyte lipids was observed after the fish-oil supplement. Ingestion of fish oil resulted in a 40% decrease in the triglyceride concentration, a 12% increase in HDL cholesterol, and a significant decrease in plasma viscosity, whereas the vegetable-oil placebo had no significant effect. We conclude that a moderate intake of fish oil (15 g/d) is a feasible treatment for hypertriglyceridemia even in patients with a background of high linoleic acid intake and that it may have a beneficial effect on several cardiovascular risk factors. 