Typing for HLA-D determinants, using primed lymphocyte typing (PLT), has been compared to the results obtained using conventional homozygous stimulating cell primary MLC tests. The HLA-Dwl, -Dw2 and -Dw3 specificities were studied. Preliminary results indicate that these two methods essentially type for the HLA-D determinants and that reproducible results can be obtained employing the PLT technique after 24 hours of incubation in the secondary cultures.