A new technique for reducing bleeding during partial hepatectomy has been investigated in dogs. It consists of producing systemic hypotension using trime-thaphan alone, and in combination with Vasopressin. Hypotension of 20 minutes and resection of 35 per cent of liver substance produced minimal bleeding and insignificant effects on liver function. Further studies are in progress to determine the effects on liver function of hypotension up to 45 minutes in duration and to learn the significance of liver shunts and sphincter mechanisms. Preliminary results are briefly discussed. The hepatic artery flow is dependent on mean aortic pressure. The clinical usefulness of this technique is discussed.