We have recently described a "new" private HLA-DR antigen, DR"LTM", which has a frequency of approximately 0.6% in Danes. Primed Lymphocyte Typing (PLT) cells directed towards DR"LTM"-associated determinants were generated in vitro by haplotype primings in two unrelated families with DR"LTM" positive individuals. Both PLT-cells reacted in parallel and gave positive reactions with (i) two unrelated and (ii) eight related individuals, all of whom were DR"LTM"-positive. Both PLT-cells gave negative reactions with (i) 38 unrelated and (ii) 15 related DR"LTM"-negative individuals. Thus, there was total agreement between the results obtained by HLA-DR typing with the antiserum "LTM" and by PLT-typing with these two haplotype primed PLT-cells. None of the DP"LTM"-positive individuals carried more than one of the antigens HLA-Dw/-DRw/DP1-8 and the local specificity D/DP"H". Accordingly, this "new" PLT-defined antigen, DP"LTM", most probably belongs to the series of HLA-D/DR-associated DP-antigens previously described.