['To characterize the host response to hepatitis B virus (HBV) infection in human hepatocytes transplanted into immunocompetent rodent rats tolerized by, and transplanted with primary human hepatocytes.', 'One week after the transplantation, rats were inoculated with HBV, and viral gene expression, replication, and host response was monitored.', 'HBV DNA was detectable in serum for at least 60 days. HBsAg levels rose steadily for 3 weeks post-inoculation and then plateaued at a level of about 0.6 pg/ml. HBV RNA was also found in liver at levels that remained constant through the time course. Immunofluorescence revealed clusters of hepatocytes that stained positive for HBcAg. The presence of HBV covalently closed circular DNA (cccDNA) in liver was demonstrated using nuclease digestion of single-stranded DNA followed by PCR. Serum ALT levels rose and reached a peak level of 180 IU/L on day 18, but remained elevated for 60 days. Histology revealed a progressive predominantly mononuclear lobular hepatitis.'] Does hepatitis B virus infection of transplanted human hepatocytes cause a biochemical and histological hepatitis in immunocopetentent rats?