The author studied the adrenotropic receptors of the non-pregnant uteri of the rabbit and rat, using epinephrine (alpha and beta activator), phenoxybenzamine(alpha blocking agent) and nethalide (beta blockade), and obtained the following results: 1. The spontaneous motility of isolated non-pregnant uteri from rabbits were stimulated by epinephrine, whereas that of isolated non-pregnant rat uterus was inhibited by epinephrine. 2. Both alpha and beta adrenergic receptors were present in the uterine muscle of both animals. 3. In the non-pregnant rabbit uterus, alpha receptors were predominant, whereas in the non -pregnant rat uterus, beta receptors preponderated over alpha receptors