Changes in lobar volume of the liver and in total hepatic function were studied in 19 patients with biliary tract cancer who underwent right portal vein embolization as preoperative management for extensive liver resection. Computed tomography (CT) was performed to estimate liver volume before and approximately 11 days after embolization. An indocyanine green (ICG) test was performed before and 11 to 13 days after embolization. The calculated volume of the right lobe decreased from 761 ± 181 cm3 to 625 ± 110 cm3 11 days after embolization (P < .0001), whereas the volume of the left lobe increased from 420 ± 94 cm3 to 555 ± 110 cm3 (P < .0001). Thus, portal embolization produced a gain in left lobe volume of 136 ± 62 cm3 and an almost equivalent loss in right lobe volume. The hypertrophy ratio of the left lobe, expressed as percentage of postembolization volume of the left lobe to preembolization size, of the 5 patients with diabetes mellitus (DM) was lower than that of the 14 patients without diabetes (116.7 ± 6.3% vs. 140.4 ± 18.4%; P < .005). The ICG disappearance rate in 16 patients improved from 0.163 ± 0.163 ± 0.034 to 0.177 ± 0.027 (P < .05). The improvement was especially evident in 9 of 14 postjaundice patients, although the rate decreased slightly in 2 patients without jaundice. We conclude that right portal vein embolization can produce a compensatory hypertrophy of the left lobe within 11 days without seriously affecting hepatic function. In diabetic patients, however, a longer interval between embolization and operation may be needed to achieve sufficient hypertrophy of the left lobe. (HEPATOLOGY 1995;21:434–439.)