<jats:p> Codeine is an analgesic commonly used to relieve pain in the early post partum. Its metabolite, morphine, is probably responsible for its effectiveness in this use. However, morphine may also cause neonatal apnea. We studied free codeine and morphine levels inbreastmilk of 17 samples from seven mothers and neonatal plasma of 24 samples from 11 healthy, term neonates. <jats:p> Levels were determined by radioimmunoassay. Milk codeine levels ranged from 33.8 to 314 ng/ml 20 to 240 minutes after codeine; morphine levels ranged from 1.9 to 20.5 ng/ml. Infant plasma samples one to four hours after feeding had codeine levels ranging from <0.8 to 4.5 ng/ml; morphine ranged from <0.5 to 2.2 ng/ml. <jats:p> Low infant plasma levels are secondary to low excretion into milk and the small amounts of milk available in the first few days. Moderate codeine use during this time (<four 60 mg doses) is probably safe.