111Indium leucocyte scans were performed on 26 patients with active rheumatoid arthritis. An abnormal localization of radioactivity was observed in the gut of 12 of these patients, generally in the region of the terminal ileum, caecum and ascending colon. No difference was found in the intake of nonsteroidal anti-inflammatory drugs between those with positive and negative scans. Two patients with positive scans were on no medication. These observations suggest the possibility of a primary role for a gastrointestinal lesion in the aetiology of rheumatoid arthritis, although these abnormalities could be secondary or unrelated.