Previous studies in mice and monkeys suggested that either splenic irradiation of splenectomy led to enhanced allogeneic marrow engraftment. These findings suggested that a population of radiation-resistant host cells involved in mediating marrow graft rejection are sequestered in the spleen. In this current study, the effect of splenectomy in dogs receiving 9.2 Gy total body irradiation (TBI) and unrelated dog leukocyte antigen (DLA)-nonidentical donor marrow grafts was studied. We found that splenectomy did not significantly change the incidence of graft failure as compared to that observed in previously and concurrently transplanted nonsplenectomized recipients.