Models of HBsAg specific cell mediated lympholysis have been developed and utilized to examine the cytotoxic T lymphocytes (CTL) in hepatitis B patients. Procedures are being developed to establish antigen specific T lymphocyte cell lines. One T cell clone has been isolated from HBV vaccine recipient by repeated alternated stimulation with antigen and interleukin 2. Its antigenic specificity and HLA restriction have been established. The HLA restriction has been mapped and the T cell specific antigenic site at primary structural level is being sought after with synthetic polypeptides.