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Dr. Mehmet Şükrü Sever Ataköy, 4. Kisim, TO Blok No: 216, D:15 Bakirköy İstanbul (Turkey) Dear Sir, The kidneys (together with the liver) are responsible for most of the metabolism of polypeptide hormones; furthermore some hormones such as calcitonin (CT) and the N-terminal fragment of parathyroid hormone (PTH) are not metabolized by the liver, hence the role of the kidneys becomes more important [1]. On the other hand, it is yet unclear, whether nonfunctioning allografts take part in hormone metabolism either in posttransplanta-tion acute tubular necrosis or in the phase of irreversible rejection. During the investigation of the resolution of secondary hyperparathyroidism in 12 cadaveric renal allograft recipients, we noted an interesting finding. Serum levels of immunoreactive parathyroid hormone (iPTH) and CT were significantly lower in the early posttransplanta-tion period compared with pretransplantation values (table 1). All of these recipients suffered posttransplanta-tion acute tubular necrosis and were treated with supportive dialysis. Therefore, we concluded that the improvements in hormone levels were due to the contribution of nonfunctioning allografts to iPTH and CT metabolism. Serum levels of these hormones were not significantly lower in 2 patients with evidence of absent blood supply, as would be expected. In the second part of the trial, serum levels of iPTH and CT were measured in 15 patients who had irreversible rejection 1–18 months before the study, and did not have transplant nephrectomy. These values were compared with the same parameters of patients undergoing dialysis in our center, and were found to be significantly lower (table 1). Two of the dialysis patients had been transplanted three years before, and suffered rejections 2 and 4 months, respectively, thereafter. These patients’ serum iPTH and CT levels were very high, similar to the levels of Table 1. Serum levels of iPTH and CT before and 2 weeks after cadaveric renal transplantation, and in dialyzed patients with and without rejected allografts