Liver fibrosis determines the course and prognosis of chronic liver disease. Histological examination of liver biopsy is essential for diagnosing hepatic disease. Evaluation of serum concentration procollagen III peptides (sPIIIP) by radioimmunoassay (RIA) is a biochemical test useful for evaluating a fibrotic process. We have investigated 20 healthy subjects and 50 patients with chronic liver disease, histologically diagnosed by percutaneous liver biopsy: steatosis (8), fibrosteatosis (7), chronic persistent hepatitis (10), chronic active hepatitis (7), cirrhosis (18). SPIIIP levels were increased in patients with cirrhosis and chronic active hepatitis and in these groups of patients such levels were well correlated with histological activity of hepatic disease. Evaluation of serum concentration of PIIIP by RIA seems to be a useful test for evaluating a fibrotic process in chronic liver diseases evolving towards cirrhosis.