Spontaneous uterine contractility during the menstrual cycle is required for menstruation, gamete transport, and, most likely, embryo nidation. Abnormal uterine contractility has been linked to dysmenorrhea, a condition associated with painful uterine cramping. Based on previous studies with progesterone, we have postulated the existence of a portal system that is responsible for some degree of direct vagina-to-uterus transport of administered compounds (i.e., the "first uterine pass effect"). It is possible that treatment with uterorelaxing substances, particularly beta-adrenergic agonists, may alleviate the uterine discomfort that accompanies dysmenorrhea. However, side effects encountered with oral administration of beta-agonists limit their utility. Alternatively, vaginal delivery of beta-agonists could solve this dilemma by enhancing their efficacy and reducing side effects. Therefore, in the current study we used hysterectomy specimens and an in vitro uterine perfusion system to test the vagina-to-uterus transport of [3H]terbutaline, a well-known beta-agonist. With the use of autoradiographic and scintillation counting techniques, our results clearly show progressive diffusion of labeled terbutaline from the rim of vaginal tissue through the uterus during the first 12 hours of perfusion. This indicates that uterine targeting of terbutaline can be accomplished through vaginal administration, suggesting a new therapeutic modality in women's health care.