40 patients with sonographically detected diffuse liver diseases of different severity and 8 controls with normal ultrasound of the liver were evaluated for fasting concentrations of serum bile acids (SBA) using an enzymatic method. Differences of SBA levels were significant among 4 groups classified as to severity by ultrasonography; SBA levels above 4.6 mumol/l were specific for the more severe grades of liver disease. Measurement of SBA and the evaluation of echographic patterns may be helpful in the decision to perform a liver biopsy.