Liver biopsies from 52 patients with chronic hepatitis B were investigated for the presence and distribution of HBcAg and the results were compared with the status of hepatitis B virus deoxyribonucleic acid (HBV-DNA). The patients consisted of 37 men and 15 women, aged 16-55 years (mean = 34 years). Serum alanine aminotransferase (ALT) was elevated in 50 patients (range: 18-969 U/L; mean = 290 U/L). Serological testing showed HBsAg in all, HBeAg in 45 (87%), and HBV-DNA in 28 (54%). Liver biopsies demonstrated HBcAg in 35 (67%) patients. HBcAg was not only present in 31 of 45 (69%) patients who were seropositive for HBeAg, but also in four of seven (57%) with antibody to HBeAg (anti-HBe). In 28 of 35 (80%) patients with HBcAg in the liver, serum HBV-DNA was detected. However, no serum HBV-DNA was detected in 17 patients who had no detectable HBcAg in the liver. The distribution of HBcAg in the liver was rather cytoplasmic and nuclear than nuclear alone. Among 33 patients with cytoplasmic HBcAg in the liver, 15 (45%) had an evidence of acute exacerbation of hepatitis with marked ALT elevation (range: 168-894 U/L; mean = 385 U/L) and nine patients showed severe chronic active hepatitis and confluent necrosis, histologically. These results indicate that the presence of HBcAg in the liver correlates with the amount of circulating hepatitis B virus as quantified by serum level of HBV-DNA. The predominant cytoplasmic HBcAg in the liver may suggest the possibility of multiple episodes of acute exacerbation and more severe ongoing hepatitis during the clinical course.