Eight women having cesarean section under general anesthesia received vecuronium (VCB) 0.01 mg.kg-1 as a priming dose, followed 180 s later by 0.11 mg.kg-1 as an intubation dose. Subsequently, VCB concentrations of umbilical venous and maternal arterial blood at delivery were assayed. The time from the injection of intubation dose to delivery was 283 +/- 55 (mean +/- SD) s. Umbilical and maternal VCB concentrations at delivery were 79.4 +/-36.1 1ng.ml-1 (UV) and 1258.3 +/- 464.1 ng.ml-1 (MA). respectively. Thus, the umbilical venous to maternal arterial VCB concentration ratio (UV.MA-1) was 0.07 +/- 0.02. One-min and 5-min Apgar scores were 8-9 and 9-10, respectively. Judging from previous reports concerning VCB administration during cesarean section, total of VCB 0.12 mg.kg-1 may be an overdose. We concluded therefore that of total VCB 0.10 mg.kg-1 seems to be an appropriate dose for cesarean section.