In order to prevent the local recurrence of malignant tumors, it is important for surgeon to maintain a sufficient margin between the tumor and the edge at resection. For this reason we do not use an auto-suturing device, but instead use the ultrasonic cutting and coagulating system (HARMONIC SCALPEL, ETHICON ENDO-SURGERY Cincinnati, Ohio) whenever we perform either a segmental resection or a wedge resection of the lung. The subjects investigated consisted of 24 cases of lung tumors (15 metastatic tumors, 5 cases with primary lung cancer, 3 inflammatory tumors; and one benign tumor). The type of operation included 10 segmental resections and 14 wedge resections, with 21 open thoracotomies and 3 instances of thoracoscopic surgery, while 15 were single resections and 9 were multiple resections. Little bleeding was seen at the resection of the parenchyma and the vessels of the lung. However prolonged air leakage was observed in some cases that needed pleurodesis. The mean duration time of the surgery was 266 minutes, and the mean blood loss was 173 ml. The operative duration was a little longer than normal, because many cases were not first thoracotomies and some cases had multiple tumors. Nevertheless the amount of blood loss was slight. The longest post-operative period was two years and six months, no local recurrence has yet been seen in any of malignant cases. We consider this system to be very effective for performing a resection of the lung parenchyma because of the reduced blood loss and the apparent increased prevention of recurrence.