The side effect profile of sulphasalazine was documented in 200 patients with inflammatory joint disease treated with the drug for at least 1 year. Fifty-eight percent of patients developed one or more adverse reactions and in 21.5% the drug was withdrawn. A further 28% continued taking the drug at a reduced dose. Five percent of the side effects were judged to be potentially serious. In all patients the reactions subsided on either discontinuation of the drug or reduction of the dose. Gastrointestinal (33%) and central nervous system reactions (19%) were the most common, but all were relatively minor. Neutropenia (2%), thrombocytopenia (1%) and pan-hypogammaglobulinaemia (1%) were potentially the most serious effects. The side effect profile of sulphasalazine in inflammatory joint disease appeared to be similar to that in inflammatory bowel disease, but reactions were more frequent in inflammatory joint disease. Enteric-coated sulphasalazine is a useful addition to the small number of slow acting antirheumatic drugs, and in view of its established efficacy, its level of toxicity was found to be 'acceptable' as long as patients were carefully monitored and regular blood tests were carried out.