Background. The spleen is considered to be an important secondary lymphoid organ where acute graft-versus-host disease (GVHD) is initiated by donor T cells that recognize host alloantigens after allogeneic bone-marrow transplantation (BMT). The influence of splenectomy on the development of GVHD prior to BMT has yet to be determined. Methods. The mortality and severity of murine GVHD of unsplenectomized, splenectomized, and sham-operated recipients of allogeneic BMT were compared in a blinded fashion. Serum levels of interferon (IFN)-γ were measured 7 days after BMT, as an index of systemic donor T-cell responses. Results. Mortality and morbidity of acute GVHD were not significantly affected by splenectomy in a major histocompatibility complex (MHC)-mismatched, CD4-driven murine GVHD model and a minor histocompatibility antigen (MiHA)-mismatched, CD8 driven GVHD model. Serum levels of IFN-γ also were not different between the groups. Conclusion. GVHD can readily develop after allogeneic BMT, even in the absence of the spleen, in these mouse models.