HLA-DR typing results of 47 skin transplant donor-recipient pairs were analysed. HLA-A, B, and C typing and mixed lymphocyte culture (MLC) testing was also included in this study. Skin transplants exchanged between HLA-A-, B-, and DR-identical, MLC-negative donor-recipient pairs had the longest graft survival (mean survival time, 17 days), whereas skin grafts exchanged between completely nonidentical donor-recipient combinations had the shortest survival (mean survival time, 10 days). Because of the correlation between identity for the DR antigens and the low or nonreactivity in the MLC test, identity for DR will predict a better skin graft survival than nonidentity. It was concluded that the best match between donor and recipient of a graft, using only serological techniques, is one where there is identity for HLA-A, B, and DR.