The presence of hepatitis B virus (HBV) genome, transcripts, and antigens (HBsAg, HBcAg, HBeAg) was examined in peripheral blood lymphocytes (PBL) from 12 patients with HBsAg-positive (B) chronic active hepatitis (CAH) and 8 normal donors by Southern and Northern blot techniques and enzyme-linked immunoassays (ELISA). HBV DNA was detected in 5 patients with B-CAH as extrachromosomal, full-length monomers of 3.2 kb. In 3 of these patients Northern blot analysis revealed the presence of the 3.6-3.8 kb RNA species, which were accompanied in one case by the HBsAg-specific 2.4 kb transcript. An ELISA performed on cell lysate obtained from this patient showed low but detectable amounts of HBsAg as compared to control PBL incubated with up to 50 micrograms/ml of the viral antigen. Serum HBV DNA was found in 3 patients with B-CAH, whereas all individuals positive for cellular HBV DNA had circulating HBeAg. These data indicate that lymphocytes from some patients with hepatitis B can harbor a transcriptionally and translationally active HBV genome.