The excretion of ketobemidone into human breast milk was investigated in three women who obtained ketobemidone as postoperative pain relief after Cesarean section and two women premedicated with 5 mg of ketobemidone before currettage after delivery. The highest observed concentration of ketobemidone in breast milk was 36 ng/ml three hours after administration, and 4-7 hours after administration the concentration was 3-5 fold that in maternal plasma. It could be estimated that the newborn will be exposed to less than 2 micrograms of ketobemidone during the first 24 hours.