Thirty-eight morbidity obese patients undergoing gastric bypass were divided into two groups. All patients received general endotracheal anesthesia with muscle relaxation and controlled respiration with N2O-O2 mixture. In addition, group I, 17 patients, received balanced anesthesia, while the remaining 21 patients, group II, received thoracic (T-5) epidural analgesia. Postoperative analgesia was achieved with morphine intravenously in group I and with 0.5% bupivacaine epidurally in group II. Circulatory function was measured and calculated using radial artery cannulation and pulmonary artery catheterization with Swan-Ganz thermodilution catheters. A significant decrease in cardiac index (10% and 14% in groups I and II, respectively), in left and right ventricular stroke work (12% to 30%), systolic blood pressure-heart rate product (16% and 28% in groups I and II, respectively), in arterial venous oxygen content difference and oxygen consumption (31% and 39% in groups I and II, respectively) was observed during surgery. A decrease in intrapulmonary shunt from 20% +/- 2.9% before anesthesia to 15% +/- 2.1% intraoperatively was seen in patients given epidural anesthesia. Postoperatively epidural analgesia was associated with a decrease in left ventricular stroke work 12%), systolic pressure-heart rate product (10%), arteriovenous oxygen content differences (17%), and oxygen consumption (20%), compared with values observed when patients experienced pain. Morphine given for relief of postoperative pain was not associated with significant changes in cardiovascular function. Continuous epidural analgesia used postoperatively for relief of pain in morbidity obese patients, following upper abdominal surgery, slightly decreases oxygen requirement and benefits cardiovascular function as reflected by a decrease in left ventricular stroke work.