This study was undertaken to determine the effect, if any, of ranitidine on bupivacaine disposition in 28 women undergoing cesarean section. Before epidural anesthesia, ranitidine (50 mg IM) or sodium citrate (30 mL orally) was administered to groups of 14 parturients each. Ranitidine was administered 2 h before epidural anesthesia and sodium citrate was administered 10 min before the epidural. Maternal plasma samples were collected after epidural anesthesia with bupivacaine. A total of 15 maternal plasma samples were taken from the time of administration of epidural anesthesia up to 180 min. Postpartum plasma and urine samples were also collected from both mothers and neonates. Plasma samples were collected up to 48 h postpartum at intervals of 12, 24, and 48 h. Urine samples were collected at six 6-h intervals up to 36 h postpartum. A two-way analysis of variance with repeated measures demonstrated that there was no significant difference in bupivacaine levels between the maternal plasma curves of the ranitidine and the control groups. At the time of delivery, plasma levels of bupivacaine and its N-dealkylated metabolite PPX (2,6-pipecolylxylidine) were no different in the mothers or neonates of either group. There was no significant difference in plasma protein binding of bupivacaine in the presence of ranitidine. The excretion rates of bupivacaine and PPX were not measurably influenced by ranitidine. The amount of bupivacaine excreted, the amount of metabolite excreted, and the percentage of drug excreted as metabolite in maternal urine were not significantly different. These data indicate that there is no measurable effect of ranitidine on the disposition of bupivacaine in parturients.