A previous study using the hairless mouse model demonstrated that diets containing a fish-oil lipid source, which contained high levels of omega-3 fatty acids, markedly increased the minimum erythema dose (MED) when compared with diets containing other polyunsaturated fatty acids. To determine whether fish oil supplementation could produce a similar effect in humans, 20 subjects were randomized into two groups, a placebo group and a group receiving fish-oil supplements over a 4-week period. Results showed a small, but statistically significant, increase in MED in patients whose diet was supplemented with fish oil. Cholesterol and prostaglandin E2 levels were unchanged, while triglyceride levels were significantly decreased in the fish oil group. No significant changes in any of these parameters occurred in the placebo group.