The bone metabolism was evaluated in 20 patients after successful transplantation of the kidneys. In case of a functional graft within 22 months after transplantation of the kidneys complete regression of histological signs of secondary hyperparathyroidism was found, i.e. of fibrous osteodystrophy with a decline of the osteoclastic absorption and in 50% of the patients bone histology revealed osteomalacia. On the X-ray of the skeleton in 65% signs of osteoporosis were found, incl. 10% where the results were in discrepancy with the histological finding. The normal plasma calcium level before and after transplantation of the kidney was not affected. Other basic indicators of bone metabolism--phosphates, alkaline phosphatase, the bone isoenzyme of alkaline phosphatase and parathormone attained normal levels within 22 months after transplantation. Bone fluorides remain elevated also after 22 months following successful transplantation of the kidneys, although significantly less than before.