A technique for the direct measurement of portal vein pressure in fully conscious patients is described. This uses a percutaneous transhepatic approach with a thin Chiba needle and is shown to be simple and safe. The technique has been applied to 123 patients with a variety of liver disorders and the pressure measurements have been compared with those obtained by the indirect technique of wedge hepatic vein catheterization. Close agreement was found between portal vein pressure and wedged hepatic vein pressure in quiescent alcoholic liver disease and alcoholic hepatitis. In chronic active hepatitis, portal vein pressure tended to be higher than wedged hepatic vein pressure, indicating a presinusoidal component to the portal hypertension. This technique is shown to be useful in assessing idiopathic protal hypertension and in demonstrating hepatofugal flow.