Specific antibodies to the RNA-dependent DNA polymerase (reverse transcriptase) of murine type C viruses have been isolated from the renal glomeruli of both leukemic and nonleukemic AKR mice where they presumably had been deposited as immune complexes. The antibodies were shown to have sedimentation coefficients of 26S to 28S and 5S to 7S on sucrose rate zonal centrifugation. Inactivation with monospecific antisera to various mouse immunoglobulins identified antibodies as being in both immunoglobulin (IGM) and IgG classes. In addition, these antibodies only reacted with the reverse transcriptase from murine and feline type C viruses, but not the polymerase from avian myeloblastosis virus (AMV). Our results provide additional evidence for the lack of immunological tolerance and demonstrate the presence of another immune complex system in AKR kidneys.