AbstractThe inhibitory effects of HLA‐D ‐associated antisera on stimulating lymphocytes when cultured together with allogeneic primed responding lymphocytes were investigated. The responding lymphocytes were primed for either the HLA‐Dw2 or Dw3 determinants. The presence of HLA‐D ‐associated (la‐like) antibodies during the culture period specifically inhibited the stimulatory capability of lymphocytes possessing the HLA‐D determinants with which the antisera were apparently reacting, as long as the stimulating cells carried the determinant for which the responding cells were primed. HLA‐D ‐associated antisera of other specificities caused no decrease in the stimulatory capability. These antisera, therefore, apparently contain antibodies which are reactive with determinants closely associated or identical to the HLA‐D determinants and may be human analogues to th