144 patients with severe rheumatoid arthritis from six centres were randomised to receive oral cyclosporin or placebo for 6 months. The initial daily dose of cyclosporin was 2.5 mg/kg, which was increased cautiously with monitoring of serum cyclosporin levels and creatinine; the mean stabilisation dose was 3.8 mg/kg. There were significant improvements in the cyclosporin-treated patients compared with the controls in the major outcomes of reduction of active joints (23% improvement), pain (24%), and functional status (16%); global improvement was 27%. In the cyclosporin group serum creatinine increased by a mean of 15.6 mumols/l and mean arterial blood pressure by 6.27 mmHg; these increases were controlled in all but 2 patients by dose adjustment without withdrawal from the study.