The intermittent intravenous administration of narcotic analgesics had advantages over intramuscular administration, but is often impracticable. The design of a prototype apparatus is described, from which analgesic, pethidine, can be self-administered intravenously during labour. The apparatus consists of a syringe pump and control system from which the patient can demand an increment of analgesic. The minimum interval between increments and the dose of the increment are preset. A demand for analgesia is only successful when the patient passes a reaction-time test, subsequently modified. The apparatus has been used by forty-two mothers in labour. The mean total dose self-administered (2.2 mg/kg) was well within the prescribed limits, suggesting that mothers regulated their demand. The apparatus appears acceptable and safe in labour. The apparatus will probably be of value in comparative studies of analgesics.