α-melanocyte stimulating hormone (MSH) induces the differentiation of mouse epidermal melanocytes in vivo and in vitro. Adrenocorticotropic hormone (ACTH) possesses the same amino acid sequence as MSH does. α-MSH induces the differentiation of mouse epidermal melanocytes in vivo and in vitro. ACTH (4-11) loses almost all activity for the binding to melanocortin receptor 1 (MC1R).