Little is known about the pharmacology of the metabolites of 2-chloroprocaine in obstetrical patients. The primary objective of this study was to describe the elimination of 2-chloroaminobenzoic acid (CABA) in maternal and neonatal urine after epidural anesthesia. A secondary objective was to compare its elimination in patients with preterm and term deliveries. The study included 21 pregnant women and their offspring. The mean gestational age of the 11 preterm infants was 34 +/- 3 weeks and that of the 10 term infants was 40 +/- 2 weeks. Maternal and cord venous blood samples were obtained at delivery and 12-hr urine samples for 72 hr postpartum. Blood and urine samples were analyzed for CABA by gas chromatography using electron capture detection. Both mothers and neonates excreted considerable amounts of unchanged CABA, and mothers also excreted CABA in a conjugated form. Mean elimination rate constants were 0.263 +/- 0.193 mg X hr-1 for mothers and 0.129 +/- 0.035 micrograms X hr-1 for neonates. Over 95% of the CABA recovered from the mothers and neonates was excreted by 36 hr postpartum. Mothers excreted 40% of the administered 2-chloroprocaine as CABA and neonates excreted 0.22-0.25% of the maternal dose as CABA. No differences in elimination due to the length of gestation were found in the mothers or neonates. Although mothers excrete CABA more rapidly than neonates, the results of this study suggest that both effectively excrete CABA.