The effectiveness of epiphyseal distraction was investigated in vivo and in vitro by forces applied to the distal femoral growth plates of New Zealand white immature rabbits. Distraction forces of 5N and 10N were applied every 3 days to the distal growth plate of the right femur in vivo, in 16 rabbits Four weeks later the length of all distracted femurs was significant longer than both the length of control side and the same one of group ON. Histological study showed hyperplasia of the growth plate, an increase in chondrocytes division rate, and no evidence of epiphyseolysis. The in vitro breaking forces of the growth plate were measured after in vivo distraction. The mean breaking force of the distracted side was not lower than mean values for the undistracted control side. Sixteen femora from 8 rabbits underwent epiphseal distraction in vitro, with 20N, 60N and 100N forces. the mean plastic deformation of the growth plate was great in connection with increasing traction. The subsequence breaking force of these growth plates was no influenced. The results obtained in this study indicated that limb lengthening might be achieved by chondrodiatasis with the proper distraction force and/or a slow distraction rate.