The optimal method of transecting liver parenchyma has not been established and presently a variety of methods are in use. In a controlled study in pigs standard resections were performed with four different transection techniques: ultrasonic dissection, suction dissection, electrocautery, and sharp dissection. The blood loss, number of vessels identified before their division, need for additional hemostatic measures, and time for each procedure were evaluated. Also, the histologic appearance of the fresh and the healing cut surface of the liver was studied. The blood loss was the lowest when ultrasonic dissection was used (median blood loss of 58 ml per resection). The comparisons with suction dissection (median blood loss of 87 ml) and cautery (median blood loss of 79 ml) were not significant. The ultrasonic and suction dissection techniques were both effective in isolating vessels, but the ultrasonic dissector did this more atraumatically. Cautery and ultrasonic dissection had a hemostatic effect on the parenchyma in that a significantly smaller number of vessels needed to be clipped or tied. On histologic study of the fresh cut liver surface, a smooth surface was seen with ultrasonic dissection, parenchymal hemorrhage after suction dissection, and coagulation necrosis after electrocautery. Ultrasonic dissection was the only technique that combined lowered blood loss because medium- and large-size vessels were dissected free and ligated before transection and a hemostatic effect on small vessels.