To assess the clinical relevance of transforming growth factor β1 (TGF-β1) in chronic liver disease, urinary TGF-β1 and circulating aminoterminal propeptides of type III procollagen (PIIINP) levels were determined by radioimmunoassay in 100 cirrhotic patients, 44 patients with chronic hepatitis, and 50 healthy controls. TGF-β1 and PIIINP levels in cirrhotic patients were higher than those in patients with chronic hepatitis (each P < .0001) or healthy controls (each P < .0001), respectively. There was a correlation between TGF-β1 and PIIINP levels in patients (r = .858, P < .0001). The higher the urinary TGF-β1 level, the worse the severity of chronic liver disease (P < .001). TGF-β1 levels in cirrhotic patients with antibodies to hepatitis C virus (anti-HCV) were higher than in those without (P <.0001). Compared with cirrhotic patients with hepatitis B surface antigen (HBsAg) alone, those with HBsAg and anti-HCV had higher TGF- β1 levels (P < .001), a higher frequency of raised TGF-β1 (P < .005), and a higher frequency of patients with Child-Pugh C (P < .005). Multivariate analysis indicated that the TGF-β1 level was significantly correlated with the presence of cirrhosis. In conclusion, urinary TGF-β1 levels may be used as a marker for hepatic fibrogenesis. Higher urinary TGF-β1 levels correlate with more severe liver disease.