Carbonated bupivacaine, plain bupivacaine hydrochloride, and bupivacaine hydrochloride with adrenaline were used to provide epidural analgesia for patients undergoing vaginal hysterectomy. Following injection the blood concentrations of bupivacaine were measured at intervals over a period of 30 minutes. All three preparations produced satisfactory analgesia at a bupivacaine dose of 1.5 mg/kg body weight. The highest group mean blood concentrations were just outside the toxic dose range. Carbonated bupivacaine was absorbed most rapidly producing significantly higher blood concentrations up to 12 minutes after injection.