The effect of prophylactic minitracheostomy on the incidence of postoperative atelectasis and pulmonary gas exchange was evaluated in a prospective, random control study of 29 patients undergoing thoracotomy. Fourteen were randomly allocated to have a minitracheostomy, which was done in the recovery room immediately after operation, and the remainder acted as controls. Increased radiodensity and atelectasis were seen more often on the chest radiographs of the control patients on the first (p less than 0.05) and on the seventh postoperative days (p less than 0.01), irrespective of the extent of the pulmonary operation. Bronchial lavage under general anaesthesia or sedation was required by 6 of the 15 control patients, but by none of those who had had a minitracheostomy (p less than 0.05). These results support the hypothesis that minitracheostomy is a useful adjunct to postoperative care after thoracotomy.