A study was performed to determine the efficacy and feasibility of using fish oil capsules for treatment of moderate hypercholesterolemia. Thirty-three subjects, randomized to fish or olive oil, took two 1-g capsules with each meal for 12 weeks. Each subject crossed over to the alternate treatment at 12 weeks. Patients maintained usual levels of exercise and diet for 24 weeks. Eight subjects dropped out. For the group starting fish oil (n = 13), the average baseline cholesterol level was 6.336 mmol/L (245.0 mg/dL) and was 6.341 mmol/L (245.2 mg/dL) after 12 weeks. High-density lipoprotein cholesterol (HDL-C) and calculated low-density lipoprotein cholesterol (LDL-C) baseline levels were 1.459 mmol/L (56.4 mg/dL) and 4.332 mmol/L (167.5 mg/dL); 1.474 mmol/L (57.0 mg/dL) and 4.479 mmol/L (173.2 mg/dL), respectively, after fish oil supplementation. In the group that began with olive oil (n = 12), baseline total cholesterol level was 6.274 mmol/L (242.6 mg/dL); HDL-C and calculated LDL-C baseline levels were 1.386 mmol/L (53.6 mg/dL) and 3.988 mmol/L (154.2 mg/dL). When mean baseline levels were compared with post-fish-oil values for the entire population, no significant change in total cholesterol or LDL-HDL ratio was obtained. Triglyceride responses to fish oil were variable. Values after olive oil treatment were neither significantly different from baseline nor different from fish oil. It was concluded that fish oil in manufacturer's recommended dosage does not appear to lower moderately elevated cholesterol levels.