Exogenous opioids in human breast milk and acute neonatal neurobehavior: a preliminary study. Opioid analgesia requirements, distribution into breast milk, and influence on neonatal neurobehavior were evaluated in ten parturient-neonate pairs nursing after elective cesarean section during epidural anesthesia. Five patients received first a loading dose of intravenous meperidine after umbilical cord clamping, then patient-controlled analgesia (PCA) with intravenous meperidine, and finally meperidine tablets as needed. Five patients received morphine in the same manner. Treatment groups showed no differences with respect to neonatal Apgar scores or visual analog scale (VAS) pain or satisfaction scores at 24 and 48 h postpartum. Breast milk specimens, obtained at 12, 24, 36, 48, 72, and 96 h postpartum and analyzed for opioids and metabolites, showed persistently elevated normeperidine concentrations in the meperidine group. A blinded psychologist evaluated each infant once on the 3rd day of life with the Brazelton Neonatal Behavioral Assessment Scale (NBAS). A priori, the "alertness" and three "human orientation" outcomes of the NBAS were chosen for analysis as best measures of opioid-induced effects. On all four outcomes, neonates in the morphine group scored significantly higher (P less than 0.05) than neonates in the meperidine group. We conclude that post-cesarean delivery PCA with morphine provides equivalent maternal analgesia and overall satisfaction as that provided by PCA with meperidine, but with significantly less neurobehavioral depression among breast-fed neonates on the 3rd day of life. 