The purpose of this study was to investigate the ability of cultured chondrocytes to prevent formation of bony bridge and possibly to repair of the damaged growth plate. Growth cartilage cells were obrained from the new born canine epiphyseal plates and was culture-expanded in high density. It took 14 days until formation of micro mass of cartilage cells which was easily removable from the culture flask. Twenty dogs were divided into two groups: group I (10), the medial side of growth plate of right proximal tibia was destroyed and cultured chondrocytes were homografted into the defect: and group II (10), the medial side of growth plate of right proximal tibia was destroyed and was left as it was. Left leg was served as a control. Serial radiological and histological observation were made until 16 weeks after homografting to determine the growth parrern. Following results were obtained. 1. In group I, 8 of 10 dogs had near normal growth with little angular deformity of the tibia, averaging 8° at post-op 16 weeks. Two dogs had 20° angulation at 16 weeks post-surgery. In contrast in group II, angular deformity was obvious at 4 weeks post-surgery, reaching 31° at 16 weeks post-surgery. 2. In group II, bony bridge was consistently formed on the medial side of the proximal tibia. In group I, the cultured chondrocytes initially appeared to be an amorphous cartiagenous mass, which, however, remained to contribute to matrix formation as time went on. 3. This study showed the ability of cultrued chondrocytes to prevent formation of bony bridge and possibly to repair the damaged growth plate. To prove the effectiveness of homografting of the growth cartilage cells for reconstruction of the growth plat, further studies should be followed.