The study was to confirm the osteogenic potential of fibroblasts. The split-thickness skin of rabbit was processed into small ships that were used for in vitro culture and then subjected to histochemical and radioautographic observation. Fibroblasts swam out from the chips, increased in number, became confluent and formed multi-layer structure. The fibroblasts excreted innumerable tiny granules, heaping up on the cell body and merging gradually into foggy substances. These foggy substances kept on enlarging and formed round or oval nodules that connected into thin trabecular structure. Histochemical study of the nodules and trabecular structures with specific new bone labelling tetracycline and alizarin red S revealed positive reaction. This implied that the nodules and trabecular structure were bone tissues. Again, after labelling with ³H-TdR, the cultured fibroblasts were injected into radius fracture site of the same rabbits. Radioautographic study of the fracture callus on the 21st post-fracture day revealed osteocytes bearing silver grains. This signified that in the course of fracture healing fibroblasts had transformed into osteocytes. The above-mentioned results indicate clearly the osteogenic potential of the rabbit dermal fibroblasts.