The effects of three supplemental doses of fish oil on plasma lipids, lipoproteins, and bleeding times were studied in ten hypertriglyceridemic patients. After a 3-wk baseline period each patient was given 15, 25, or 40 mL fish oil/d (containing 4.5, 7.5, and 12 g n-3 fatty acids) for three successive 6-wk periods, each separated by a 4-wk period of no supplementation. Plasma cholesterol concentrations decreased from 7.40 mmol/L to 6.35, 6.55, and 6.40 mmol/L with increasing doses of fish oil (p less than 0.01 vs baseline for each). Plasma triglyceride concentrations decreased from 6.10 mmol/L to 2.90, 2.80, and 2.35 mmol/L (p less than 0.01 vs baseline for each). Low-density-lipoprotein cholesterol concentrations increased significantly (by 23% and 28%) with the two higher doses, respectively. Bleeding times increased only with the largest dose. The lowest dose was the most hypolipidemic per gram n-3 fatty acids.