Because the liver is of considerable importance in metabolism of thyroid hormones, plasma levels of thyroxine (T4), triiodotyronine (T3) with their unbound fractions (FT4 and FT3), reverse T3 (rT3)--an inactive isomer of T3-tyrotropin (TSH) and TSH response to thyrotropin releasing hormone (TRH; 250 micrograms i.V.) were determined by radioimmunoassays in 50 clinically euthyroid patients with alcoholic cirrhosis. T4 mean concentration (7.3 micrograms/dl) did not differ from normal values but T3 was decreased (101 vs 154 ng/dl; p less than 0.001) and was correlated with the degree of liver damage appreciated by a clinico-biological index. FT4 was elevated in patients (17.1 vs 13.1 pg/ml; p less than 0.02) although FT3 was slightly decreased (3.4 vs 4.5 pg/ml; p less than 0.10) with an increased FT4: FT3 ratio (7.0 vs 3.0; p less than 0.02). rT3 was elevated (592 vs 206 ng/100 ml; p less than 0.001) and correlated with FT4/FT3: rT3/T3 ratio (p less than 0.01) and with the severity of the cirrhosis. Basal TSH levels (3.3 microU/ml) and TSH responsiveness to TRH was normal though very scattered, and independant from T3 and T4 values. It may be concluded that: 1. euthyroidy in cirrhosis assessed by a normal responsiveness to TRH, results from a compensatory increase in FT4. 2. The low T3 and FT3 levels may proceed from an impairment of peripheral T4 in to T3 conversion with a deviation pathway towards rT3. 3. T3 and rT3 levels provide valuable index of the severity of the cirrhosis.