BACKGROUND: The influence of labor epidural fentanyl on the neonate is controversial. The purpose of this study was to determine whether epidural fentanyl has an impact on breast-feeding. METHODS: Women who previously breast-fed a child and who requested labor epidural analgesia were randomly assigned in a double-blinded manner to one of three groups: (1) no fentanyl group, (2) intermediate-dose fentanyl group (intent to administer between 1 and 150 microg epidural fentanyl), or (3) high-dose epidural fentanyl group (intent to administer > 150 microg epidural fentanyl). On postpartum day 1, the mother and a lactation consultant separately assessed whether the infant was experiencing difficulty breast-feeding, and a pediatrician assessed infant neurobehavior. All women were contacted 6 weeks postpartum to determine whether they were still breast-feeding. RESULTS: Sixty women were randomly assigned to receive no fentanyl, 59 were randomly assigned to receive an intermediate dose, and 58 were randomly assigned to receive high-dose fentanyl. On postpartum day 1, women who were randomly assigned to receive high-dose fentanyl reported difficulty breast-feeding (n = 12, 21%) more often than women who were randomly assigned to receive an intermediate fentanyl dose (n = 6, 10%), or no fentanyl (n = 6, 10%), although this did not reach statistical significance (P = 0.09). There was also no significant difference among groups in breast-feeding difficulty based on the lactation consultant's evaluation (40% difficulty in each group; P = 1.0). Neurobehavior scores were lowest in the infants of women who were randomly assigned to receive more than 150 microg fentanyl (P = 0.03). At 6 weeks postpartum, more women who were randomly assigned to high-dose epidural fentanyl were not breast-feeding (n = 10, 17%) than women who were randomly assigned to receive either an intermediate fentanyl dose (n = 3, 5%) or no fentanyl (n = 1, 2%) (P = 0.005). CONCLUSIONS: Among women who breast-fed previously, those who were randomly assigned to receive high-dose labor epidural fentanyl were more likely to have stopped breast-feeding 6 weeks postpartum than woman who were randomly assigned to receive less fentanyl or no fentanyl.