Serum levels of the tissue inhibitor of metalloproteinases-1 (TIMP-1) were measured in 268 patients with liver diseases by means of a one-step sandwich enzyme immunoassay. In the cases of acute hepatitis, chronic active hepatitis (CAH), liver cirrhosis (LC) and hepatocellular carcinoma (HCC), the levels of TIMP-1 were higher than those of the control group. Tissue inhibitor of metalloproteinases-1 levels correlated with type III procollagen peptide and with type IV collagen, indicating TIMP-1 as a useful marker for hepatic fibrosis. Levels of TIMP-1 also correlated with aspartate aminotransferase and alanine aminotransferase levels and showed the highest levels in acute hepatitis. Thus, TIMP-1 might also reflect hepatic inflammation. Serum levels of alpha-fetoprotein and TIMP-1 had a significant positive correlation in patients with HCC. A cut-off level of TIMP-1 between LC and HCC was set at 440 ng/mL, having a low sensitivity and a high specificity. These results suggest the usefulness of TIMP-1 as a tumour marker in cases of HCC where alpha-fetoprotein levels are not elevated.