The effects of two adrenoceptor antagonists, nicergoline (alpha 1) and acebutolol (beta 1), on the contraction of myometrium in the proestrous rat were compared to those of noradrenaline and phentolamine. The spontaneous myometrial contractions of Wistar rats on the day of proestrus were recorded isometrically and the data were analysed using Wilcoxon non-parametric statistics. All drugs were administered i.v. and the doses are expressed as microgram/kg body weight. Noradrenaline (1200 micrograms/kg per h) induced a 32.5% reduction (P less than 0.001) of the uterine contraction amplitude. Nicergoline did not alter uterine motility significantly when administered alone at doses ranging from 400 to 1600 micrograms/kg. However, successive injections of nicergoline in the same range given during noradrenaline infusion at 600 micrograms/kg per h potentiated the relaxing action of the latter (38%, P less than 0.01). Phentolamine (120 micrograms/kg) reduced myometrial activity by 25% (P less than 0.05). This inhibitory response rose to 65% (P less than 0.001) when the dose of phentolamine was increased to 960 micrograms/kg. When a single injection of nicergoline (400 micrograms/kg) was followed by the administration of increasing doses of acebutolol (120, 1200, 2400 micrograms/kg) the slight inhibitory effect on uterine motility observed after administration of each of the two agents separately became more pronounced (P less than 0.05). It appears from these results that combining noradrenaline with nicergoline and nicergoline with acebutolol leads to potentiation of their relaxing effects. Furthermore the results confirm that nicergoline is a partial alpha-blocker.