The Response of Mammalian Epidermal Melanocytes in Culture to Hormones**From the Departments of Medicine and Anatomy, Yale University School of Medicine, New Haven, Connecticut

Changes in the skin color of mammals, including man, have been brought about by the administration of certain hormones (1, 2, 3). The manner in which the hormones act at the cellular level is not yet clear. In this report, the effects of four hormones on normal adult guinea pig melanocytes in tissue culture are described. The hormones are alpha melanocyte-stimulat-ing hormone (a-MSH), acetylcholine, norepinephrine, and melatonin.