Five patients with secondary hyperparathyroidism (2(0) HPT) due to chronic renal failure were investigated for PTH metabolism kinetics after total parathyroidectomy and autograft at the forearm (PTxG). We studied the kinetics of PTH for 24 hours after surgical treatment and gradually increased PTH levels when the parathyroid grafts became functional. It has been well known that the secreted intact PTH is peripherally cleaved in the region of reside 34 to yield amino- and carboxyl-terminal fragments. In this study, specific assays were used for intact PTH (INT-PTH), middle (HS-PTH, MM-PTH) and carboxyl-terminal (C-PTH) fragments. Half-lives were calculated from the mean values of all experiments by a two-compartment system; INT-PTH: 11.1 +/- 3.9 min, HS-PTH: 9.6 +/- 1.7 hrs., MM-PTH: 11.1 +/- 2.9 hrs., C-PTH: 10.1 +/- 1.2 hrs. (Mean +/- SD). The disappearance rate of biologically active intact PTH was rapid, whereas those of middle and carboxyl-terminal biologically inactive fragments were prolonged in the patients with chronic renal failure. The graft function was examined by PTH gradient between the venous samples in the grafted arm as compared to the non-grafted arm. PTH gradient of INT-PTH assay was over 1.5 one week following PTxG in all patients. This suggests that the intact PTH assay is a reliable predictor of clinical response to the graft function after PTxG.