Ninety-four renal allograft recipients receiving cyclosporin A (CsA) immunosuppression for up to 4 years were examined for the presence of viral warts, keratoses, and skin cancers. They were compared with a group of 68 recipients on azathioprine who had been matched for duration of immunosuppression and other factors that might influence the occurrence of these lesions. No difference in prevalence of these tumours was found. Viral, bacterial, and fungal infections and other disorders of the skin related to immunosuppression were also noted. Apart from hypertrichosis, which occurred more frequently in the CsA group, no differences were observed. In view of the importance of duration of immunosuppression, the relative effects on the skin of the two drugs will not become apparent until CsA has been in general use for a much longer period of time. In the early stages, however, there appear to be no differences in the dermatological side-effects between CsA- and azathioprine-treated patients.