In the treatment of severe psoriasis, cyclosporin may achieve improvement or remission at low doses, but relapse usually occurs on withdrawal of treatment. An initial dose of 3 mg/kg per day is recommended. Complete remission should not be the objective, and the role of long-term maintenance cyclosporin therapy is uncertain because of potential side-effects--especially nephrotoxicity, hypertension, and a predisposition to malignancy. Guidelines are proposed for the assessment of such treatment.