1,3-bis(2-chloroethyl)-1-nitrosourea(BCNU) (NSC 409962), an agent being tested for antitumor activity, may cause hyperpigmentation of skin. This darkening follows topical application but not systemic administration. Although evident erythema does not always precede hyperpigmentation caused by BCNU, histologic changes in the epidermis suggest that this increased melanogenesis occurs as a postinflammatory event.