Physeal distraction is used for limb lengthening or correction of deformities in skeletally immature patients. But the effect of distraction on the physis is uncertain. The young rabbits were arranged into five groups according to the slow distraction rates: Group I (no distraction), Group II (distraction rate of 0.25mm per day), Group III (distraction rate of 0.5mm per day), Group IV (distraction rate of 0.75 mm per day), Group V (distraction rate of 1mm per day). The tibial length, size of proliferating zone, microscopic findings of physis immunostained with bromodeoxyuridine, and physeal response to physeal distraction on each group were studied. The results were as follows. 1. There was an increase in bone length on the distracted side (1.8 to 4.2mm). 2. There was an irregular increase in the thickness of the distracted physis. 3. There was an abnormal accumulation of hypertrophic chondrocytes in hypertrophic zone in distracted physis. 4. There was no evidence of anomalous cell proliferation, in the resting, proliferating and hypertrophic zones. These results conclude that the physeal distraction does not stimulate cell proliferation in the physis, even when it is seen to be thickened after the chondrodiatasis.