Twenty-four patients underwent elective cholecystectomy. They were randomized into two groups, one consisting of 13 patients having CPAP* by face-mask for 4 h after surgery and the other, consisting of 11 patients serving as control. The patients were all given intravenous anesthesia and were manually ventilated during anesthesia without using PEEP. The groups were comparable as concerns sex, age, weight, smoking-habits, preoperative pulmonary status, type of surgery and anesthesia-time. The study showed that both groups had a reduction in VC and PaO2 and a high percentage of them developed chest X-ray changes. In none of the variables mentioned was there any significant difference between the groups after surgery. Hypoxemia after abdominal surgery can thus not be prevented by only using CPAP for 4 h postoperatively.