The effects of dimethylsulfoxide (DMSO) upon the topical absorption of vasopressin and adrenocorticotropin (corticotropin) in the rat and melanocyte stimulating hormone (MSH) in the frog were investigated. At a dose approximately 20,000 times that used intravenously, vasopressin absorption was slightly increased in one third of the rats by the application of DMSO, while corticotropin absorption was unaffected. The topical absorption of MSH in the frog was increased by DMSO in three of five experiments at a dose of MSH several hundred times that used in dorsal lymph sac injection. The small increase in topical absorption of these hormones seen in some animals after the application of DMSO, therefore, required extremely large doses.