Glycoprotein 90K/MAC-2BP is a member of the scavenger receptor cystein-rich protein superfamily, which is thought to be involved in immune surveillance, defending the body against pathogens and cancer. 90K serum levels are elevated in patients with cancer of various origins and in viral infections, such as human immunodeficiency virus and hepatitis C virus (HCV). Because in patients with HCV-related cirrhosis the incidence of hepatocellular carcinoma (HCC) is high, in the present paper we examined, by means of an enzyme-linked immunosorbent assay, the 90K serum levels in 103 patients with liver cirrhosis, and in 69 with HCC, and compared them to alpha-fetoprotein, the reference tumor marker for this neoplasm. Serum levels of 90K (cut-off 14 microg/ml) were elevated both in cirrhosis (39%) and HCC (46%) compared to controls (14.1 microg/ml vs. 10.6 microg/ml in cirrhosis, and 14.8 microg/ml vs. 9.1 microg/ml in HCC, p < or = 0.001). There was a significant association with the presence of anti-HCV antibodies. 90K was found to be a non-specific tumor marker which is complementary to alpha-fetoprotein on the basis of its probable different biological significance. In fact, 74% of HCC patients had at least one positive marker. Combined use of 90K and alpha-fetoprotein could improve the sensitivity of a single test in the diagnosis of HCC.