Epidemiological data have suggested that a low dose of dietary n-3 polyunsaturated fatty acids from seafood may protect against coronary heart disease. We studied the effect of supplementation with a low dose of very long-chain n-3 fatty acids (0.65 g day-1) on plasma lipids, haemostasis, and neutrophil aggregation. Twenty-four healthy subjects were randomized to supplementation with very long-chain n-3 fatty acids or a control oil for 8 weeks. Laboratory analyses were done twice before and twice at the end of the supplementation period. The supplement with n-3 polyunsaturated fatty acid did not significantly affect plasma lipids or plasma levels of fibrinogen, factor VII, plasminogen activator inhibitor, whole blood aggregation or aggregability of neutrophil leukocytes. Therefore, the potential beneficial effect of very long-chain n-3 fatty acids in coronary heart disease is likely to be mediated through other mechanisms.