Twenty dogs were subjected to allotransplantation of the lower end of the femur, frozen at -196 degrees C for 24 hours in liquid nitrogen, and stored at -30 degrees C. Two dogs were sacrificed at monthly intervals, providing the grafted bone for histological study. Eight dogs were excluded from the study following infection or death, resulting in a follow up of only 6 months. Monthly roentgenographic assessment showed bridging of the host-graft unit by the second month, with posterior subluxation of the graft with subsequent malunion. Histologically, exuberant callus was seen around the interface with progressive incorporation of the graft. However, the articular cartilage degenerated after 2 months. Attempts to repair the articular surface with new fibrocartilage were poor in the malunited grafts. The technical problems in surgery including control of infection, sound mechanical fixation and repair of tendons and ligaments must be solved to ensure a successful allograft.