Local infiltration of the perineum is a simple and commonly used technique for providing pain relief for episiotomy. It has always been considered safe and effective because a small amount of local anesthetic agent could be administered quickly and accurately to the perineum just prior to vaginal delivery and cord clamping. Because of the short time interval between local infiltration and delivery, very little anesthetic was thought to reach the fetus. However, the maternal and neonatal disposition of lidocaine following local perineal infiltration has not been well studied. The purpose of this study was to document placental transfer or nontransfer of lidocaine following local perineal infiltration. Fifteen normal parturient women at term and their infants were studied. After local perineal infiltration, the concentrations of lidocaine and two metabolites--monoethyl glycine xylidide and glycine xylidide --were determined in maternal plasma, in the umbilical cord vein at delivery, and in maternal and neonatal plasma or urine for 2 days post partum. Lidocaine and its metabolites were quantitated by gas chromatography-mass spectrometry. The pharmacologic results indicated the following: First, lidocaine is detected in maternal plasma as early as 1 minute after injection, and peak plasma concentrations occur within 3 to 15 minutes. Second, there is rapid placental transfer of lidocaine; the mean fetal/maternal ratio of 1.32 was significantly higher than that found following epidural anesthesia. Third, lidocaine and its active metabolites persisted in neonatal urine for at least 48 hours after delivery. This study suggests that local perineal infiltration with lidocaine for episiotomy should be considered similar to any other anesthetic technique in that it may result in significant neonatal drug exposure.