The uterus receives adrenergic terminals from the mesenteric ganglia and considerably large amount of catecholamines have been shown to be contained in this organ. On the other hand, the activities of epinephrine, norepinephrine or adrenergic nerve on uterine motility is so complicated that many controversial results have been reporter. Recently, a large number of reports concerning the changes of uterine catecholamines content have appeared, but little is known about the role of uterine catecholamines in their activities on uterine motility. The present experiments were undertaken to determine the significance of the intrinsic uterine catecholamines in the physiology of uterus. Female albino rabbits weighing approximately 2 kg were employed in this experiment. uterine strip3 were prepared and suspended in a constant temperature bath(38˚C) containing 100 ml of Locke s solution aerated with 95% oxygen and 5% carbon dioxide. Spontaneous motility was recorded on a smoked drum with an isotonic lever. The catecholamines concentration of the uterus was determined according to the Procedure described of Shore and Olin (1958). Human uterus obtained from patients was also used to determine the catecholam ines content of myometrium. Followings are summarized results. 1) On the non-pregnant rabbit uterine strips, epinephrine and norepinephrine significantly elevated the tonus and stimulated the spontaneous motility. Pretreatment with dichloroisoproterenol(DCI), an adrenergic beta-receptor blocker, enhanced the stimulatory activity of epinephrine or norepinephrine. On the other hand, pretreatment with dibenamine, an adrenergic alpha-receptor blocker, rendered the uterine muscle to exhibit inhibition after the administration of epinephrine or norepinephrine. Following the treatment with both DCI and dibenamine, epinephrine or norepinephrine produced no appreciable effects on the spontaneous motility of the uterus. These results suggest there exist both alpha and beta-adrenergic receptors in the uterine muscle and the response to epinephrine of the former is predominant over that of latter in the non-pregnant uterus of rabbits. The total catecholamines concentration of the non-pregnant uterus was 351 mμg/g and the fractional concentrations of epinephrine and norepinephrine were 125 mμg/g(35.7%) and 226 mμg/g respectively. It is interesting to note that the catecholamines content of uterus was characterized by a high fractional corcentration of epinephrine relative to norepinephrine. 2) On the pregnant rabbit uterine strips, the effects of epinephrine and norepinephrine varied according to the period of pregnancy. The response to epinephrine of adrenergic beta receptor of uterus increased during pregnancy, and the effect of catecholamine was inhibitory in the early pregnancy but became stimulatory as the pregnancy progressed. This stimulating action on the uterine motility was found to occur through the action of norepinephrine. The uterine catecholamines concentration was markedly reduced during pregnancy. The catecholamines concentration was started to decrease in the early pregnancy, reached the lowest level in the mid-pregnancy and then started to increaae again in the late pregnancy when the total catecholamines content became the highest level of all. This increase of catefholamines in late pregnancy was chiefly due to the increase of norepinephrine. These results suggest that the uterine motility may be related to the catecholamines content, especially norepinephrine content in the uterus. 3) Bilateral oophorectomy of rabbits results in a marked shrink of the uterus in size. The spontaneous motility of the uterine segment of these animals was very weak and irregular. Norepinephrine produced inhibitory effect, whereas epinephrine was stimulatory or inhibitory effect on the uterine segment. The total catecholamines tontent in whole uterus was markedly reduced. The injection of estr