The drug therapies for hypercalcemia of malignancy have been known to be associated with either limited efficacy or cumulative toxicity in patients with advanced renal failure. To establish the guidelines for the use of dialysis and to determine its optimal prescription for hypercalcemia, calcium-free hemodialysis was performed in 6 hypercalcemic patients with renal failure not responding enough to forced saline diuresis. Calcium-free dialysate contained sodium 135, potassium 2.5, chloride 108, magnesium 0.75, bicarbonate 30 mmol/l. Mean hemodialysis time was 160 ± 27 min and mean Kt/V urea was 0.75 ± 0.2. Plasma calcium concentrations fell from a mean value of 2.92 ± 0.21 mmol/l (range 2.55-3.25) to 2.58 ± 0.16 mmol/l at 1 h of hemodialysis and to 2.16 ± 0.33 mmol/l (range 1.63-2.53) following 2-3 h of hemodialysis. The ionized calcium (n = 4) decreased from 1.44 ± 0.14 mmol/l to 0.99 ± 0.2 mmol/l. No patient showed any hypocalcemic symptoms and signs during hemodialysis. The rate of decrease in plasma calcium did not appear to produce adverse effects in any of the patients. There was a significant positive correlation between the decrease in plasma calcium concentration and the Kt/ V urea (y = 1.4x – 0.29, r = 0.92, p < 0.01). We conclude that calcium-free hemodialysis is indicated when the presence of severe renal failure prevents the administration of large volumes of intravenous fluids to hypercalcemic patients. The amount of dialysis (Kt/V urea) can be used to predict the decrease in plasma calcium concentration during calcium-free hemodialysis.