We studied the suppression of intact parathyroid hormone (PTH) in ten patients on chronic hemodialysis using different calcium concentrations of dialysate. Secondly, giving i.v. vitamin D3 at commencement of dialysis we investigated whether 1 alpha (OH)D3 or 1,25(OH)2D3 acutely modifies the responsiveness of the parathyroid gland to the suppressive effect of increased serum calcium. Dialysis with high-calcium dialysate (1.75 mmol/l) reverted the plasma PTH to normal limits. Lower-calcium dialysate (1.5 mmol/l) induced only a partial suppression of hyperparathyroidism. We found no differences in the suppression of hyperparathyroidism whether 1 alpha (OH)D3 or 1,25(OH)2D3 was given at the beginning of the dialysis or not. We conclude that the suppressibility of hyperparathyroidism in dialysis patients can be evaluated by different calcium concentrations of dialysate, and that i.v. vitamin D3 does not acutely modify the responsiveness of the parathyroid gland to the effect of calcium.