Retrospective HLA-DR-typing and the influence of HLA-DR antigen on transplantation prognosis was studied in 90 kidney donor-recipient pairs. It was clearly demonstrated that HLA-DR compatible donor kidney provides a significantly better transplant prognosis than if there is HLA-DR incompatibility. Donor kidneys with only one identical HLA-DR antigen gave a six-month survival rate of 80%. Only HLA-AB identical cadaver kidneys ("full house identity") give similar survival times. Because of relatively lower polymorphism of the HLA-DR alloantigen system, HLA-DR identical donor organs are discovered more frequently than when HLA-AB antigens are taken into consideration. HLA-DR identical donor kidneys (identical for both HLA-DR antigens) have an even better transplant prognosis than "full house identical" kidneys, since the survival rate in the former is 87% after six months.