Ten patients with rheumatoid arthritis were entered into a 24-week pilot study of oral cyclosporin A at a starting dosage of 6 mg/kg/day, followed by a 12-week washout period. Significant improvement in clinical parameters was observed at 12 weeks and 24 weeks (P less than 0.02 versus baseline for joint pain and joint swelling indexes and patient and physician assessments; P less than 0.04 versus baseline in the numbers of painful/tender joints and swollen joints). Adverse reactions were varied: renal impairment occurred in all patients and hypertension occurred in 7. All patients demonstrated an increase in defined disease activity at cessation of treatment and through the washout period. Cyclosporin A is clinically effective in the treatment of patients with refractory rheumatoid arthritis, but its value as an intervention therapy is limited by its toxicity.