Tense ascites is a widely used clinical concept lacking a quantitative correlate. In 13 patients with tense cirrhotic ascites we measured total intraabdominal pressure (IAP), hydrostatic pressure (HP), and tension. HP was defined as the level of ascitic fluid determined by percussion of the abdominal wall, and tension was the fluid level in the manometer above the HP. The total IAP is the sum of HP and tension. At a later, second measurement 11 patients significantly decreased their IAP. As expected in early stages of ascites resolution, major changes were found to be due to the reduction of the tension component, which accounted for 68% of the decrease in IAP. The HP seemed to show a definite decline only at a late stage of resolving ascites. Five patients, two with an essentially unchanged IAP and three with declining IAP, increased their ascitic fluid volume at the second study. The most probable explanation of this phenomenon is in the transfer of fluid from the edematous splanchnic organs into the peritoneal cavity in the early phase of ascites mobilization.