Twenty-five healthy women in labour received morphine 1-1.75 mg in normal saline intrathecally. The residual pain was evaluated on a scale from 0 to 5 at 10 min (score 2.5) and at 25 min (score 1.5). After delivery the maternal and fetal plasma morphine concentrations were measured by radioimmunoassay in 14 parturients. Twenty-three women of 25 had vaginal deliveries, 20 of them without forceps. The maternal and fetal plasma concentrations of morphine were 6 ng ml-1 or less. The intrathecal (but not extradural) administration of morphine is effective and could provide an interesting alternative for pain relief in labour.