The value of intraoperative echo-contrast ultrasound (US) as compared with plain US was studied in 19 patients presenting with malignant liver tumors. The contrast medium SHU 454 was intraoperatively injected via the portal venous system or the biliary tract. Using intraoperative echo-contrast US, extremely small liver tumors could be sought in a limited area of the liver. In comparison with plain US, the former technique resulted in better demarcation of especially small tumors, which were seen as echo-poor areas in relation to the surrounding liver tissue.