A prospective randomized controlled trial was conducted in patients undergoing elective cholecystectomy to assess the value of routine chest physiotherapy. One hundred and two patients entered the study: 47 patients developed no pulmonary complications, 29 had pulmonary atelectasis and a further 26 developed chest infection. The pattern of changes in arterial oxygen tension in the period after operation supported the clinical allocation of the patients. Of 51 patients not receiving physiotherapy, 11 developed atelectasis and 19 chest infection. Of 51 treated patients, 18 developed atelectasis and seven chest infection. Routine prophylactic postoperative chest physiotherapy decreased significantly the frequency of chest infection (P less than 0.02).