A prospective study of postoperative pulmonary complications (PPC) appearing during the hospital stay was carried out in 417 patients undergoing surgery through a subcostal or midline incision. Postoperative pain was relieved either by intercostal block and centrally-acting analgesics on demand or by centrally-acting analgesics alone. Pulmonary complications were diagnosed from combined physical and radiological signs. After biliary surgery through a subcostal incision, PPC were less frequent (P less than 0.05) in patients receiving intercostal blocks (6%) than in those given centrally-acting analgesics (11%). After surgery through a midline incision, the complication rate was higher, 15-57%, and was related to the type of surgery, the highest incidence being found after partial gastrectomy and operations for malignancy, and no significant reduction in the rate of PPC after intercostal blocks with this incision was found in any age group. Indeed, an increased rate of PPC was found in our patients over the age of 60 who had received bilateral intercostal blocks. Irrespective of the type of incision, surgery or method of postoperative pain relief, the patients with PPC more often had respiratory or other disorders preoperatively or a surgical complication intra- or postoperatively than those with normal postoperative recovery. Predisposing physical factors and high age were more common among the patients developing PPC in spite of treatment with intercostal blocks compared to those without such treatment.