Altered pattern of calcium kinetics in hemodialysis patients after parathyroidectomy. Six HD patients with severe secondary hyperparathyroidism (sHPT) underwent studies of calcium kinetics prior to and after parathyroidectomy (PTX) with autotransplantation. Postoperatively, patients received vitamin D and calcium supplementation. Before PTX, a markedly elevated bone turnover was found, with increased fluxes of calcium from plasma into the exchangeable calcium pool. This pool was three times larger than normal, indicating a high risk of extraosseous calcifications. Despite a marked fall in parathyroid hormone (iPTH) levels after PTX, bone cell activity was maintained, as indicated by elevated values for Ca retention. Although Ca efflux from plasma into other compartments of the exchangeable pools remained above normal, the size of the total exchangeable calcium pool markedly decreased after PTX, indicating that PTX with autotransplantation, followed by vitamin D therapy, can normalize bone turnover and shift the balance of calcium flux towards mineralized bone. Reduction in the exchangeable calcium pool may explain the clinical finding that extraosseous calcifications regress in some patients after PTX. 