Allogeneic limb transplantation with and without immunosuppression has been successfully reported. We used the experimental model described by Fritz and colleagues to investigate the value of different factors in the rejection phase. Twenty rats of inbred strains sustained an allogeneic limb transplantation without immunosuppression. In 6 rats an isologous limb transplantation was performed as a control group. Factors investigated in the transplanted limb were glucose, lactic acid, and blood gases of the peripheral blood, as well as laser Doppler flowmeter (LDF) recordings and histology. All factors were compared with the normal contralateral limb of the rat. All rats were killed between days 2 to 14 following operation. In the allogeneic limb transplantation model in the rat, clinical and histological examination as well as LDF measurements (p less than 0.0001) are good factors for rejection. In contrast, peripheral blood gases, glucose, and lactate were not useful as factors for rejection. In this model, however, LDF values cannot predict an initial onset of the rejection before clinical signs are evident, presumably because of the impossibility of continuous measurements.