A double blind, placebo controlled trial was carried out to assess the efficacy of cod liver oil as an adjunct treatment to non-steroidal anti-inflammatory drugs (NSAIDs) in the management of osteoarthritis in general practice. Eighty six patients were given 10 ml of either cod liver oil or olive oil placebo daily as a supplement to their regular NSAID treatment for 24 weeks. Patients were assessed by their general practitioner at four week intervals for joint pain/inflammation, overall interference with activities, and unwanted effects of treatment. Patients recorded on visual analogue scales their daily pain and the extent to which arthritis interfered with everyday activities. There was no significant benefit for the patients taking cod liver oil compared with those taking placebo.