Dietary supplementation with polyunsaturated fatty acids--n-3 PUFA or fish oils--has gained increasing interest among patients suffering from rheumatoid arthritis. The biochemical background for the beneficial effects of fish oils in modulating the inflammatory response is briefly described and is partly based on findings from experimental animal models. Ten published double-blind studies evaluating the effect of a daily supplement with three to six grams of n-3 PUFA to patients with active rheumatoid arthritis are reviewed. The studies support a modest effect of fish oil on patient-reported disease parameters without serious side effects. Future research should evaluate effect, tolerance and side effects in long term studies with different daily intakes of n-3 PUFA and should also focus on the effect of n-3 PUFA in combination with standard therapy in patients with rheumatoid arthritis.