To examine bile acid synthesis in chronic liver diseases, serum total 7α-hydroxycholesterol level was measured by gas-liquid chromatography-mass spectrometry in patients with cirrhosis (n = 23), patients with chronic hepatitis (n = 21), and control subjects (n = 18). The serum 7α-hydroxycholesterol levels were significantly lower in patients with cirrhosis than the controls (78 ± 59 pmol/mL vs. 237 ± 97 pmol/mL; mean ± SD). However, in patients with chronic hepatitis, the level was fully retained (262 ± 102 pmol/mL). Serum 7α-hydroxycholesterol levels of 17 patients with cirrhosis classified as Child B and C ranged from 33 to 69 pmol/mL, and all were less than the normal range (between 104 and 466 pmol/mL), however, those levels of some patients classified as Child A were within the normal range. Serum 7α-hydroxycholesterol levels significantly correlated with serum albumin, cholinesterase, total bile acid, direct bilirubin, alkaline phosphatase, indocyanine green (ICG) retention rate, hepaplastin test, and lecithin-cholesterol acyltransferase activities. We conclude that bile acid synthesis is well preserved in patients with chronic hepatitis and that it is decreased in most patients with cirrhosis. Serum 7α-hydroxycholesterol may be a new parameter of liver function testing to assess hepatic bile acid synthesis in patients with chronic liver diseases. (HEPATOLOGY 1995; 22:1182–1187.).