Children with autoimmune chronic active hepatitis (aCAH) have preferential activation of T Lymphocytes expressing Interleukin-i receptor (IL2r) and helper/inducer (H/I) phenotype. To assess whether a similar pattern of activation is present in HBV related chronic liver disease (CLD) we studied 19 children with chronic HBV infection, 13 having biochemical and/or histological evidence of CLD. HLA-DH and IL2r expression on purified T lymphocytes was assessed by immunofluorescence with phycoerythrin conjugated monoclonal antibodies. Functional subsets of activated T-cells were studied by double-staining with fluorescein conjugated anti-cytotoxic/suppressor (C/S)(Leu2) or H/I (Leu3) monoclonal antibodies. HLA-DR positive T-cells were significantly increased both in patients with (mean±SD 13.9±7%: p<0.01 Rank Test), and without evidence of CLD (8.9±1.8%, p<0.01) when compared to 18 healthy children (2.8±2%). 59% of the HLA-DR positive cells were C/S and 37% H/I. Percentage of IL2r positive T cells was similar in patients with chronic HBV infection (1.3±1.5%) and controls(0.14±0.09%). In Chronic HBV infection there is preferential activation of T lymphocytes expressing HLA-DR and C/S phenotype. These may be the effectors of the in vitro cell cytotoxicity to autologous hepatocytes found in HBV related but not in autoimmune CLD (1). (1) Monuelli M. et al. J.Ped 1985, 106, 899-907.