Pulmonary function tests, arterial blood gas tensions and morbidity were compared in 50 patients undergoing coronary artery bypass graft surgery. Thirty patients had bilateral internal mammary grafts (Group 1), 5 patients had only saphenous vein grafts (Group 2) and 15 patients had a single arterial graft in addition to vein grafts (Group 3). Pleural effusion and wound infection were more common in patients with internal mammary artery grafts (p < 0.05). Patients in Group 2 required prolonged ventilation but this could be related to their underlying left ventricular dysfunction. Patients in all the three groups developed a severe restrictive ventilatory defect in the postoperative period and the degree of impairment was maximum in Group 1 patients (p < 0.01). These patients also had evidence of small airway obstruction. Thus an overall decrease in pulmonary function occurs in the postoperative period by 30 to 40% (p < 0.001). The derangement is greater in patients with arterial grafts, as a result of impaired blood supply, increase in pleural drains and additional surgical trauma secondary to mobilization of internal mammary arteries leading to delayed recovery. The awareness of these findings can be of great value in postoperative management of these patients. In addition, these observations should also be kept in mind while planning the choice of grafts in a patient undergoing coronary artery bypass graft surgery.