High frequency ventilation has been used experimentally and clinically in a variety of situations. This report describes two cases in which high frequency jet ventilation was used to provide adequate ventilation during thoracic surgery. A solenoid valve controlled ventilator at rates of 100 breaths/min. with a double lumen tube provided adequate gas exchange for these patients with an open chest. The minimal lung movement during high frequency jet ventilation was found to provide excellent operating conditions without undue cardiovascular embarrassment. This case report demonstrates the use of high frequency jet ventilation in two adults undergoing operation ofr pulmonary lobectomy and biopay with segmental resection.