Butorphanol (1 mg and 2 mg) and meperidine (40 mg and 80 mg), given intravenously, were evaluated for analgesic efficacy and safety in a double-blind randomized study employing 200 consenting pre-partum patients in moderate to severe pain during the late first stage of labour. Both drugs provided adequate relief of pain to the mothers. There was no significant difference in the rate of cervical dilation, the foetal heart rate, the Apgar score, pain relief or neonatal neurobehavioural scores betweeen those receiving butorphanol and those receiving meperidine. Twenty-two mothers who received butorphanol and eleven who received meperidine nursed their infants with no adverse effects observed. Side-effects were generally infrequent in this study; however, more side-effects were reported by the patients and observed by the investigator in the meperidine-treated cases (13%) than in the cases treated with butorphanol (2%).