The aim of this study was to examine and compare whole-body and segmental impedance measurements in control subjects and patients with progression of liver disease and to investigate whole-body and segmental bioelectrical changes occurring during dehydration therapy or paracentesis. Males have lower resistance (R) and reactance (Xc) values than females in measurements both of the whole body and of the arm, leg, and trunk. This is not true in patients. In the three groups of patients, whole-body R and Xc were lower in each increased disease stage, suggesting that stage has a significant main effect on impedance measurements. The lower extremities were the segment most influenced by the progression of liver disease. The sum of the arm and leg R was only slightly lower than the value of wholebody resistance. The trunk has a meager influence on this parameter, as is clearly shown by the absence of variations before and immediately after paracentesis. In edematous cirrhotic patients without ascites treated with diuretics, our data also showed a significant correlation (r = .81; SEE = 1.2) between changes in body weight (BW) and in the bioelectrical evaluation of total body water (TBW). The association of a prevalent increment of Xc (=40%) with a reduction of extracellular water is the most significant bioelectrical event during dehydration therapy. AU these findings show that impedance measurements have a low sensitivity in detecting the volume of ascites in cirrhotic patients, whereas Xc has a clinical use in monitoring changes in extracellular water (EW). (HEPATOLOGY 1995;21:352-358.) Bioelectrical impedance analysis (BIA) involves the measurement of whole-body resistance (R) and reactance (Xc). Previous studies have shown that when bioelectrical impedance is associated with other factors