Fifty male patients undergoing elective surgery for duodenal ulcer received either phenoperidine or halothane 0.5% for the supplementation of anaesthesia. The patients in the phenoperidine group required the first postoperative dose of analgesic later and had lower pain scores in the first 2 h after operation. In the course of the 1st, 2nd and 3rd days, the two groups of patients showed a similar pattern after operation with regard to pain scores, vital capacity impairment and oxygen tension measurements.