Alloreactive T-cell clones were used to study allodeterminants associated with the HLA-DR1, -DR4, and -DRw14 allelic families. Three clones derived by priming against the DR4,Dw14 alloantigen were tested against a panel of HLA-D homozygous B-cell lines and homozygous and heterozygous peripheral blood lymphocytes. Each clone was blocked by monoclonal antibodies specific for HLA-DR, but not HLA-DQ or -DP, molecules, and each showed a unique pattern of allorecognition when tested against the cell panel. Clone 14B appeared to recognize a specific sequence, termed L67-A74, comprised of amino acids in the third hypervariable region of the alpha-helix of the DR beta 1 molecule, and expressed on certain DR1-, DR4-, and DRw14-positive cells. Clone EMO25 recognized the same L67-A74 sequence, but only when expressed on DR4-positive cells, suggesting a role for residues in the first and second hypervariable regions of DR4-positive DR beta 1 molecules in T-cell recognition. Clone EM036 also recognized the L67-A74 sequence, but only when expressed on DR4,Dw14.1-positive cells, implicating residues at positions 57 and 86 of the alpha-helix in T-cell recognition. These results demonstrate the range of specific T-cell responses that are possible against alloepitopes expressed by a single class II allele (Dw14), and are an indication of the diverse regions of the class II molecule that can contribute to allorecognition sites.