One-hundred four chronic active hepatitis (CAH) patients were investigated for the expression of the hepatitis B virus (HBV) surface and core gene products (HBs Ag, HBc/HBe Ags) in peripheral blood mononuclear cells (PBMC). Two-thirds of 59 HBs antigenemic patients expressed HBs Ag in PBMC but 26% of cases positive for both anti-HBs and anti-HBc also expressed HBs Ag while none of the controls reacted. Among HBs antigenemic patients, only those who replicated HBV express the core gene products (HBc and/or HBe Ag) in PBMC, and high replicators did so more often than low replicators (P less than 0.05). The HBs Ag prevalence in PBMC, although slightly higher among HBe Ag/DNAp-positive cases could not be correlated with the intensity of HBV replication. In 16 cases (8 replicants and 8 nonreplicants) HBV DNA was detected by DNA hybridization spot test, while 8 controls devoid of HBV markers were negative. Both T and non-T cells reacted similarly for antigenic or genomic HBV markers. When the expression of HBV gene products in PBMC among 43 cases with HBs antigenemia was compared with that in the liver, a good correlation was found in 70% of cases for HBs Ag but in only 40% for HBc and HBe Ags. By contrast, among 38 cases lacking HBs Ag in the serum but positive for anti-HBc with or without anti-HBs, concordance between liver and PBMC expression of core gene products (69%) was better than for HBs antigenemic patients (40%). These data suggest that PBMC including T lymphocytes may represent the second-best HBV target and may mimic the steps of HBV cycle within hepatocytes.