HBsAg and anti-HBc, the antibody to core antigen of hepatitis B virion, were titrated by solid phase radioimmunoassay in 40 sera of HBsAg carriers with acute and chronic hepatitis and in 20 healthy subjects carrying anti-HBc alone or associated with anti-HBs. No correlation was found between HBsAg and anti-HBc titers in the single category of patients. In contrast, geometric mean titer of anti-HBc (ranging from 2(14) to 2(15)) of patients with chronic active hepatitis was significantly higher ( p = < 0.01) than that of patients with acute or chronic persistent hepatitis and healthy HBsAg carriers (ranging from 2(9) to 2(14)). Anti-HBc titer of 20 subjects without detectable HBsAg was less than 2(7). These data suggest that in subjects with persistent B virus infection, anti-HBc response is correlated with synthesis of viral genome rather than of surface antigens, so that a much higher titer of anti-HBc was detected only in patients with a more active liver disease.