Serum T3, T4, FT3, FT4 TSH and TBG concentrations were measured in 27 clinically euthyroidal patients with hepatic cirrhosis. In spite of clinical euthyroidism, the serum T2 was below the lower limit of the normal range in 21 cases (77.8%), there was low FT3 in 12 cases (44.4%), and low T3 in 4 cases (14.8%). Low T3 in the presence of normal T4, designated as "low-T3-syndrome", was present in 17 cases (63%); low T3, with low T4, designated as "low-T4-syndrome", was present in 4 cases (14.8%). Serum FT4 and TSH concentrations were in normal ranges with the exception of a few cases in which serum FT4 or TSH levels were slightly elevated. Serum T3/T4 ratio was markedly decreased, FT3% and FT4% were distinctly increased, TBG concentration was elevated. The presence of low serum T3 was significantly correlated to ascites and collateral circulation. In the cirrhotic patients with complications, such as bleeding due to rupture of the esophago-gastric varicosities, hepatic coma and cancer of liver, serum T3 concentration and T3/T4 ratio were much lower than those without such complications. Serum T3 concentrations was positively correlated with serum albumin concentration, and negatively correlated with serum bilirubin. It is concluded that determinations of serum T3, FT3, T4 are helpful for the estimation of severity of illness and prognosis in hepatic cirrhosis, and measurement of serum FT4 is useful for the differential diagnosis of euthyroidism and hypothyroidism.