Severe postoperative pain, which may persist for up to 3 days and may lead to postoperative complications, due to the patient's inability to breathe deeply and cough, is frequently experienced in the area of the incision and chest tubes by thoracotomy patients. Eighteen patients undergoing routine thoracotomies were tested preoperatively for arterial blood gases and pulmonary function and given chest x–rays. Anesthesia consisted of thiopental, succinylcholine, N2O, enflurane, and pancuronium. Before incision closure, 6 intercostal spaces were injected by the surgeon with 3 ml of a randomly determined drug mixture. Patients received either bupivacaine and saline solution, bupivacaine and LMW dextran 40, or saline and LMW dextran 40. Arterial blood gases, pulmonary function, chest x-rays, narcotic dosage, sensory level, and subjective responses were evaluated for 3 days postoperatively. Results demonstrate that intercostal nerve blocks can markedly reduce postoperative pain and improve pulmonary function in such patients. Significant differences from controls were seen in Paoz, Paces, vital capacity, forced expiratory flow rates, analgesic requirements, and patient comfort. The duration of the block with bupivacaine and saline was less than 12 hours, while the mean duration of the block with bupivacaine and dextran 40 was 36 hours.