[en] The control and influence of the stimulating DRw antigens on primed lymphocyte typing (PLT) response was studied by using a discriminatory PLT assay with a low responder: stimulator ratio. Positive restimulation was established at 90.3% RR, based on a statistical evaluation of a composite or %RR values from 13 separate intrafamily PLTs performed in this laboratory. Two intrafamily PLT cells were then made against specificities HLA-DRwl and HLA-DRw3 and restimulated with a panel of unrelated individuals. The results show a very high correlation (p < 0.001) between the HLA-DRw antigen specificity of those unrelated panel cells that stimulated in PLT and the HLA-DRw target specificity, which shows that PLT reactivity is strongly influenced by HLA-DRw