Recently developed technologies to clone alloreactive human lymphocytes have provided a powerful tool for the immunogenetic analysis of the HLA region. Alloreactive T cell clones can be used as specific reagents for HLA encoded cellular determinants detected in secondary proliferation assays such as the primed lymphocyte test (PLT) and, in cell-mediated lympholysis (CML). Lymphocyte clones can also be used for functional assays (e.g., for suppressor or helper activity) to determine the influence of HLA specific restriction.