A microsurgical model was developed to study the transplantation of large sections of vascularized skeletal tissue in inbred rats. A modified vascularized leg graft, consisting of the distal femur, knee joint, and intact tibia, with the associated musculature, was orthotopically transplanted in Fischer F344 rats. The femoral artery and vein were anastomosed by means of a micro-surgical technique. Skin coverage was accomplished with recipient skin. In the studies reported here, syngeneic grafts were followed for up to twelve months by means of clinical examinations, X-rays, bone scans, and histologic studies. The bone and-joint tissues not only survived but grew; the joints functioned and appeared to be histologically normal. Nonvascularized control grafts rapidly developed necrosis and osteomyelitis that lead to death of the recipients. Nonvascularized knee joint grafts, which were performed as additional controls, were better tolerated than nonvascularized limb grafts bat they developed progressive degenerative changes. Thus, only the vascularized grafts restored optimal limb function. This model will be useful for exploring the feasibility and potential uses of large vas-cularized grafts of skeletal tissue.