Xylazine has been characterized as a selective alpha 2-adrenoceptor agonist, which has explained its central nervous system depressant and other pharmacological effects. In order to characterize the effect of xylazine on uterine motility during the oestrus cycle in goats, intrauterine pressure changes were recorded in cycling goats using balloon-tipped catheters placed in the uterine horns and connected to pressure transducers and a recorder. The effect of xylazine on myometrial activity was studied by giving increasing doses of the drug (1.0, 10.0, 100.0 or 500.0 micrograms/kg) intravenously (i.v.) to animals either in the follicular or the luteal phase of the cycle. To establish the subtype of alpha adrenergic receptor mediating the action of xylazine, goats were pretreated with either prazosin (1.0 mg/kg, i.v.) or yohimbine (1.0 micrograms/kg, i.v.). To establish whether the effect of xylazine was pre- or post-synaptic, xylazine (100 mg/kg, i.v.) was administered to goats pretreated with reserpine (0.8 mg/kg, i.p.) to deplete presynaptic catecholamine stores. Xylazine induced a significant and dose-dependent increase on uterine motility in cycling goats, apparently mediated by post-synaptic alpha 2-adrenoceptors.