The transmission of a retrovirus by the transplantation of allografts of connective tissues was studied in a feline model with use of the feline leukemia virus, a retrovirus with a replication cycle and pathological characteristics similar to those of the human immunodeficiency virus. The retrovirus was used to infect four specific-pathogen-free cats that were subsequently used as tissue donors. Fresh allografts of menisci, patellar ligaments, and patellar ligament and bone composites were harvested from infected donors and were transplanted into the knee joints of twelve specific-pathogen-free cats. A fresh cancellous-bone allograft was transplanted into the proximal part of the tibia of four additional specific-pathogen-free cats, which served as positive control animals. Additional grafts from infected donors were harvested and were stored at -80 degrees Celsius for ten weeks. A fresh-frozen graft was then transplanted into the knee of twelve other specific-pathogen-free cats. Samples of plasma were obtained weekly from all twenty-eight cats and were tested with both an enzyme-linked immunosorbent assay to detect the presence of viral antigen and an immunofluorescent antibody assay to determine exposure to the virus. All types of fresh and fresh-frozen connective-tissue allografts from the infected donors resulted in transmission of the retrovirus to the recipient cats. The recipients had evidence of viral antigen or rising antibody titers as early as two weeks after the transplantation. Histological examination of specimens of the allografts revealed normal incorporation of the transplanted tissues, with no sign of rejection of the graft.