An endoscopic pressure sensor has been evaluated in the measurement of oesophageal variceal pressure and its response to drug ingestion. The variceal pressure showed a highly significant correlation with the splenic pulp pressure (r = 0.97) in six patients with liver disease of diverse aetiology and with hepatic venous wedge pressure (r = 0.92) in eight alcoholic cirrhotic men. Intraduodenal infusion of isosorbide dinitrate in the cirrhotics produced no change in wedge pressure or endoscopic variceal pressure despite profound falls in arterial systolic pressure. Thus isosorbide dinitrate appears to be of no value in treating portal hypertension. This study establishes the endoscopic pressure sensor as a valuable tool in screening drugs in this condition.