Summary. 6-Hydroxydopamine, when injected at 14:00 h on Days 21 and 22 of pregnancy in the rat (2 × 50 mg/kg), markedly decreased plasma and uterine noradrenaline concentrations ( − 60% and −82% respectively; P < 0·001). As a consequence of this treatment, there was severe disturbance in the distribution pattern of parturitions: 61% of rats had suppressed parturition and 31% of rats displayed a lengthened or interrupted labour. A bolus dose of prazosin (3 mg/kg) administered at 12:00 h on Day 22 completely blocked the normal process of parturition throughout the next 6 h, a result which is compatible with the half-life of the drug (2·9 ± 0·8 h). Administration of phentolamine (3 mg/kg) at term induced a significant decrease of uterine activity (frequency × duration of bursts of spike potentials) as revealed by electromyographic recordings in vivo. These results suggest that noradrenaline released from sympathetic nerve terminals interacts with α-adrenoceptors located post-synaptically to improve the overall excitability of the myometrium at the onset of labour.