Four patients with severe psoriasis have been treated with oral cyclosporine for 6 months. Two had generalized erythroderma and two had extensive plaque-type psoriasis; all had either become unresponsive to or were unable to use other accepted treatments. All four patients responded rapidly and were completely clear of psoriasis within 3 weeks of beginning therapy. Initial doses ranged from 7.5 to 8.5 mg/kg/day. Mild reversible nephrotoxicity occurred in the one patient whose cyclosporine trough level briefly exceeded 200 ng/ml. Cyclosporine may offer an alternative therapeutic modality in the management of erythrodermic or severe resistant plaque-type psoriasis. The effectiveness of cyclosporine in psoriasis underscores the putative role of cell-mediated immune factors in the pathogenesis of psoriasis.