Cyclosporin A is a new immunosuppressive agent that selectively affects T helper cells without suppressing the bone marrow. Cyclosporin A. has been used primarily to prevent rejection in organ transplantation and acute graftversus-host disease. Studies suggest that it may be of benefit in psoriasis, pemphigus vulgaris, bullous pemphigoid, Behçet's disease, and collagen vascular disorders. Since cyclosporin A has a potentially important use in dermatology, and since a number of dermatologic side effects are seen as a consequence of its use, it is important that dermatologists be familiar with this drug.