Until now the determination of fibrotic processes in liver disease was restricted to histological examination of liver tissue. Recently a RIA was developed to determine the procollagen-type III-peptide concentrations in biological fluids. We used this RIA to measure the serum procollagen-type III-peptide concentrations in patients with chronic liver disease. Additionally in 24 patients with chronic persistent and chronic active hepatitis the collagen content in liver biopsies was determined histomorphometrically. The serum procollagen-type III-peptide concentrations in healthy controls (n = 40) were 6.4 +/- 0.6 ng/ml, in chronic persistent hepatitis (n = 47) 8.7 +/- 0.5 ng/ml, in chronic active hepatitis (n = 53) 20.8 +/- 2.9 ng/ml, and in alcoholic cirrhosis of the liver (n = 22) 47.7 +/- 6.1 ng/ml. Thus the patients with chronic active hepatitis and cirrhosis of the liver showed significantly elevated serum procollagen-type III-peptide levels. In chronic hepatitis a highly significant correlation (p less than 0.001) could be demonstrated between collagen content in liver tissue and serum procollagen-type III-peptide concentrations. The determination of serum procollagen-type III-peptide concentrations may prove a new useful parameter in biochemical evaluation of liver disease.