We describe a case of liver cirrhosis lacking the expected increase in serum thyroxin (T4)-binding globulin (TBG) despite abrupt, severe increases in aspartate and alanine aminotransferases (ASAT and ALAT) in serum. Sequential change in serum T4, triiodothyronine (T3), and TBG concentrations were also measured retrospectively in serum of 10 hospitalized patients with acute viral hepatitis. Although their mean T4 and TBG concentrations significantly exceeded those in 40 normal subjects (P less than 0.002 and P less than 0.001, respectively), these values were within the normal reference intervals in five patients. ASAT and ALAT concentrations were not significantly different in patients with increased TBG and patients with normal TBG, whereas mean concentrations of serum albumin and cholinesterase and mean prothrombin times (in percent) in the former group were significantly higher than those in the latter group (P less than 0.05, P less than 0.05, and P less than 0.001, respectively). For 60 samples with increased ASAT and ALAT, TBG and albumin or cholinesterase correlated significantly (r = 0.49, P less than 0.001 and r = 0.50, P less than 0.001, respectively), but not TBG and ASAT or ALAT. Collectively, these results suggest that the increase in serum TBG in acute hepatitis may reflect its synthesis in regenerating hepatocytes rather than a simple leakage from damaged hepatocytes.