Cyclosporine (cyclosporin A) is an immunosuppressant that selectively acts on the CD4+ subset of T lymphocytes. Recent results of experimental in vitro and in vivo studies, as well as evidence obtained through the clinical use of cyclosporine in humans, strongly suggest that cyclosporine may exert a direct effect on the growth of several epithelial cell types. Thus, cyclosporine, while stimulating the growth of hair follicle keratinocytes with a resulting hypertrichosis, appears to exert a cytostatic effect on several epithelial cell types of human and animal origin. This antiproliferative effect is shared by some minimally immunosuppressive or nonimmunosuppressive cyclosporine analogues, suggesting that the molecular mechanisms that modulate epithelial cell growth differ from those responsible for immunosuppression. This newly discovered pharmacologic property of cyclosporine may hopefully lead to the wider use of nonimmunosuppressive cyclosporines in the treatment of hyperproliferative epidermal diseases.