In this pilot study, 43 patients with rheumatoid arthritis ingested 1 g of cod liver oil (one capsule) daily for 3 months. Decreases occurred in morning stiffness (52.4%; P<10(-3)), painful (42.7%) and swollen (40%) joints (P= 10(-3) each), and pain intensity (67.5%). Ratings of "good" or "very good" were awarded by 68% of the patients for efficacy and by 95% for tolerability. Eleven patients reported nonsevere adverse effects that in 3 cases may have been related to the study preparation. Cod liver oil can be recommended for the treatment of rheumatoid arthritis.