To study the role of cell-mediated immunity in chronic hepatitis B (cHB) we have cloned T cells from liver biopsies of 14 patients with cHB. As a first step, T cell lines were established from lymphocytes infiltrating the liver by culturing the biopsied specimens with autologous feeder cells and interleukin 2 (IL2). Fifty-eight clones obtained by limiting dilution showed phenotypic stability over periods of 2-26 weeks. Of the 58 clones 50 were of the "cytotoxic/suppressor" T cell subset (CD8) as defined by the monoclonal antibody T811. Only 8 of 58 clones were of the "helper/inducer" phenotype (CD4) as defined by the monoclonal antibody T151. Functional studies on 9 clones (7 of CD8+ phenotype, 2 of CD4+ phenotype) revealed high cytotoxic activity of all of these clones in a lectin-dependent cell-mediated cytotoxicity assay reflecting the killing capacity of cytotoxic T lymphocytes. All 9 clones lacked significant natural killer activity, while two additional CD8+ clones that also expressed the VEP13 antigen showed significant natural killer activity. For none of the clones tested could killer cell activity (ADCC) be demonstrated. The studies demonstrate that the clonal expansion of T lymphocytes from liver biopsies of patients with cHB in the absence of detectable antigen is possible. The propagation of in vivo activated cytolytic T lymphocytes points to an active role of these cells in the pathogenesis of this disease.