Sulphasalazine was administered to 48 patients with reactive synovitis (RS) and ankylosing spondylitis (AS) with peripheral arthritis, resistant to nonsteroidal anti-inflammatory drugs. Thirty-seven patients underwent an ileocolonoscopy and in 33 patients signs of chronic or active inflammation of the ileum and/or ileocecal valve were found. Forty-two patients improved after 3 to 12 months of treatment; 50 per cent of them went into remission. In most of the patients improvement failed to occur in the first 2 months of treatment. There was no recurrent disease activity in patients responding to the treatment. Adverse reactions were rare and did not necessitate interruption of treatment. The beneficial effect of sulphasalazine in the treatment of RS and AS with peripheral arthritis needs to be confirmed in double-blind controlled studies.