Kidney transplantations were performed in unrelated, immunosuppressed rhesus monkeys matched for two DR antigens and given five pretransplant transfusion of whole blood. The host-donor combinations were either reactive or nonreactive in mixed lymphocyte culture (MLC) and shared up to three A and B locus antigens with their blood and kidney donors. Although previous monkey experiments had shown a definite positive influence of DR matching as well as of pretransplant transfusions on graft survival, this was not found in the current experiments (the mean survival time for the MLC responsive group was 21.3 days for the MLC nonresponsive group 28.2 days). It appears therefore that the combination of pretransplant transfusions and matching for DR antigens does not have an additive or synergistic effect on graft survival. In fact, the prominent transfusion effect demonstrated previously may have been somehow compromised by matching for DR antigens. Alternatively, the clearly positive effect of matching for two DR antigens may have been reduced or lost as a consequence of giving the blood transfusions.