We recovered anti-murine retroviral hybridomas from the spleen cells of (B6 x D2) F1 mice in which graft-versus-host reaction (GVHR) had been induced by the infusion of spleen cells from either parent. The antibodies were specific for envelope proteins of endogenous retroviruses, and have provided a convenient way of classifying viruses based on their host range. They also have revealed considerable serologic heterogeneity within each host-range group. We have utilized these antibodies to characterize endogenous envelope glycoproteins in uninoculated mice. In this report I have attempted to synthesize the results of studies carried out by a number of senior investigators as well as postdoctoral fellows who have graced the Laboratory of Persistent Viral Diseases over the last 10 years. Some of the information on the nature of the endogenous glycoproteins expressed within the hematopoietic compartment of DBA/2 and C57BL mice has provided a basis for speculation, offered at the end of the report, on the possibility that anti-retroviral autoantibodies generated during the course of GVHR may be antigen-driven.