Total and conjugated biliary acids were determined in a lot of 105 subjects, including 15 healthy persons, 60 with acute viral hepatitis, 10 with chronic evolutive hepatitis, 10 with cholecystophaties and dyskinesia and 10 with obstructive jaundice. A marked diminution in the proportion of conjugated biliary acids was found in acute hepatitis and cholecystopathies. Chenodioxycholic and dioxycholic acid increase in acute diseases of the liver, whereas cholic acid increases in obstructive jaundice and chronic hepatitis, with a consecutive almost threefold reduction of th ratio of trihydroxycholanic to dihydroxycholanic acids in acute lesions of the liver cells. The ratio of glycoconjugated acids to taurocholic acids is smaller inchronic hepatitis and diseases of the gallbladder than in acute hepatitis and obstructive jaudice. Study of these ratios may represent an element of differential diagnosis in diseases of the liver and viral hepatitis. Determination of the biliary acids may have a prognostic value since an increase in these acids persists with the hepatic lesions. Determination of the biliary acids is technically difficult and may be used for diagnostic purposes only within the context of other hepatic explorations.