Epidemiologic and biochemical studies have suggested an anti-inflammatory effect of n-3 fatty acids. Beneficial therapeutic effects reported from small patient groups need to be confirmed in large-cohort controlled clinical trials. There is a growing number of clinical trials of n-3 fatty acid supplementation in disease. Clinical benefits have been moderate in patients with rheumatoid arthritis and with arterial hypertension. Clearly negative results have been reported during the past 2 years for patients with lupus nephritis and for patients with psoriasis or with atopic dermatitis. Such trials have now been completed. For patients with coronary artery disease following coronary angioplasty, earlier results of a large meta-analysis, could not be confirmed. For patients with IgA-nephropathy and for patients following kidney transplantation, a clear benefit was seen in patients receiving fish oil. These promising results are currently pursued in follow-up phase III clinical trials.