In order to study bone metabolism after renal transplantation we measured serum levels of parathyroid hormone (PTH) and osteocalcin (OC), a specific biochemical parameter of bone formation, in 30 patients with functioning kidney grafts and 30 sex- and age matched control subjects. Serum levels of OC and PTH were markedly elevated in the kidney transplantation patients when compared with the control subjects (p less than 0.0001). Elevated levels of OC and PTH were present even in patients with very well functioning transplants. In the kidney transplantation patients, a significant positive correlation between serum OC and serum PTH levels could be found. Our data give evidence of persistent hyperparathyroidism and increased bone turnover in patients after renal transplantation.