To assess the effect of thoracic epidural analgesia (TEA) on postoperative respiratory function and pulmonary complications, a prospective randomized trial was conducted in patients undergoing cholecystectomy. One hundred patients were allocated to TEA (n = 30), TEA + general anesthesia (TEA + GA) (n = 30), or general anaesthesia (GA) (n = 40) groups. Respiratory function was analysed by measuring forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), functional residual capacity (FRC), total lung capacity (TLC), peak expiratory flow (PEF) in the supine and sitting postures, and arterial blood gases. Postoperative pulmonary complications were carefully documented. TEA significantly prevented the postoperative deterioration of respiratory function as compared with general anaesthesia. FVC, FEV1 and PEF decreased by 20% in patients receiving TEA, in contrast to 55% in patients after GA on the day of operation. This improvement continued until the 2nd day after operation, when FVC, FEV1 and PEF and their recovery rates were equal in all groups. In the sitting posture the preoperative FVC, FEV1 and PEF were about 10% greater than in the supine position. After operation, this difference was further increased. The preoperative difference of 27% in FRC between the sitting and supine postures was maintained after operation. PaO2 decreased by 0.8 kPa after TEA, by 1.5 kPa after TEA + GA with the lowest value on the 2nd postoperative day and by 1.5 kPa after GA, with the lowest value immediately after operation. Simultaneous hypercarbia indicated hypoventilation, which may have contributed to impaired respiratory function on the following days.(ABSTRACT TRUNCATED AT 250 WORDS)