An animal model for testing substances that might prevent alopecia induced by oxazaphosphorines has been developed. It is based on the fact that the rat pups experience virtually total hair loss following administration of oxazaphosphorines. Using this model, we showed that epicutaneous treatment with sodium thioglycollate prevented ifosfamide-induced hair loss on the treated area. These experiments indicate that prevention of oxazaphosphorine-induced alopecia in man may be achieved by topical thiols.