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We conducted a double-blind, placebo-controlled crossover study to determine the effects of fish oil supplementation on blood pressure in middle-aged men. Subjects were randomly assigned to consume either 20 g of fish oil or safflower oil for 12 weeks and then consume the other oil for an additional 12 weeks after a 4-week washout period. We found no significant changes from the pretreatment value in systolic or diastolic blood pressure with the use of fish off supplements. In addition, there were no significant differences in the post-treatment blood pressures comparing the fish and safflower oil phases of the study. (Am J Public Health. 1993;83:267-269), Fish oil supplements do not appear to reduce high blood pressure. Of 38 middle-aged men, 15 had high blood pressure and 23 had normal blood pressure. Half of the participants took 20 grams (g) of fish oil for 12 weeks and the other half took 20 g of safflower oil for 12 weeks. Following a four-week rest period, the groups then switched and took 20 g of the other oil for 12 weeks. There were no significant changes in blood pressure following fish oil supplementation in either the men with normal blood pressure or the men with high blood pressure. Furthermore, fish oil supplementation did not significantly lower blood pressure more than safflower oil. Both the fish oil and safflower oil supplements were associated with belching, loose stools and other gastrointestinal symptoms. Studies with larger doses of fish oil have also produced mixed results, and larger doses are expensive, high in calories and can cause diarrhea and bloating.