Seventy HBsAg-positive patients, including 24 with primary hepatocellular carcinoma, 34 with chronic active hepatitis, 12 with chronic persistent hepatitis and 30 asymptomatic healthy hepatitis B virus carriers were tested for anti-HBc IgM using the Corzyme-M test. Anti-HBc IgM was detected in 50% of the primary hepatocellular carcinoma patients, 26.5% of the chronic active hepatitis patients, 25% of the chronic persistent hepatitis patients, but in none of the healthy hepatitis B virus carriers. There was no correlation between the presence of anti-HBc IgM and HBeAg, hepatitis B virus DNA, ALT or α-fetoprotein levels in either the chronic active hepatitis or chronic persistent hepatitis patients. However, a significantly higher positive rate of anti-HBc IgM was noted in the HBeAg-positive or HBV DNA-positive primary hepatocellular carcinoma patients than in those with negative markers of viral replication, but no correlation was noted between the presence of anti-HBc IgM and serum ALT or α-fetoprotein levels in these primary hepatocellular carcinoma patients. Also, no differences in positivity for HBeAg, HBV DNA or levels of serum ALT were noted when patients with high titers of anti-HBc IgM were compared to those with low titers. Thus, anti-HBc IgM cannot distinguish between HBsAg-positive patients with chronic active hepatitis, chronic persistent hepatitis or primary hepatocellular carcinoma, does not correlate with serum ALT or α-fetoprotein levels and is only associated with markers for viral replication in primary hepatocellular carcinoma patients. Based on this, anti-HBc IgM appears to have a limited usefulness for diagnosis of either chronic hepatitis B or primary hepatocellular carcinoma. Since anti-HBc IgM was negative in all our asymptomatic healthy hepatitis B virus carriers, its detection in these individuals may indicate an underlying chronic liver disease which would merit further diagnostic investigation.