The matching of donors and renal graft recipients for human leukocyte antigens A, B, and DR has been shown to exert beneficial effects on the outcome of transplantation. Until the advent of polymerase chain reaction amplification-based genotyping, the effect of HLA-DP compatibility on graft survival could not be thoroughly investigated. HLA-DP compatibility has been determined in three living-related transplants and 34 cadaveric transplants for donor-recipient pairs matched for HLA-DR and -DQ. The effect of DP mismatching on graft survival and function was assessed. No clear benefit from matching donor and recipient for HLA-DP could be discerned.