Sulphasalazine (SASP) has recently become established as an effective treatment for active rheumatoid arthritis (RA), but has not previously been used in psoriatic arthritis in which remission-inducing drugs have proved disappointing. In this one year open study, 34 patients with active psoriatic arthritis were treated with sulphasalazine. An overall favourable clinical response was observed in 23 patients (67%). Nine patients (26%) achieved a very good therapeutic response and these either had arthritis associated with spondylitis or the symmetrical type of joint disease. Evaluation at 3, 6 and 12 months showed a significant improvement in inflammatory indices including a reduction in the C-reactive protein level and ESR. The drug was well-tolerated and side-effects were mild. Eight patients (23.5%) stopped the drug because of reactions and one patient with a rash was successfully desensitised. Fifty-three percent continued the drug into the second year. No apparent exacerbation of the psoriasis was observed. These results suggest that sulphasalazine is a safe and potentially effective drug in the treatment of psoriatic arthritis. A double-blind placebo-controlled trial has been set up to determine its true efficacy.