On the day of expected delivery, primigravid rats received 0.5% bupivacaine continuously through a chronically implanted intrathecal cannula to produce intense sensory and motor blockade below the T10 level. The mean duration of delivery was prolonged to 3.1 h compared with 1.4 h in a control group without intrathecal blockade and a group which received an intrathecal infusion of Hartmann's solution. The mean percentages of live births per litter surviving the first 6 h was 94% in the control groups and 42% in those receiving bupivacaine by intrathecal infusion. No increased perinatal mortality was observed in another control group receiving an i.p. infusion of 0.5% bupivacaine in the same dose as that given intrathecally. Two mother rats died during delivery under spinal blockade because of prolonged labour. It is concluded that, without obstetric intervention, intense sensory and motor blockade delayed parturition and increased fetal mortality in the pregnant rats.