The effects were compared of sodium fluoride and calcidiol on the remodeling of the rib cortical-endosteal surface of dogs treated with prednisone for long time periods. The study used a histomorphometric and tetracycline labeling methods. It was found that administration of sodium fluoride with calcidiol and calcium carbonate limited in a higher degree than the treatment with calcidiol and calcium carbonate the development of the osteoporotic changes induced by glucocorticoids. This included reduced enhancement of the bone resorption surface, increased bone formation surface and osteoid thickness connected with acceleration of mineralization rate. The changes induced by sodium fluoride had a favorable effect on the ratio of the resorption to the formation process at the sites of bone remodeling.