The optimal dialysate calcium (Ca) concentration for hemodialysis (HD) patients is set at 2.5 mEq/L according to Kidney Disease Outcomes Quality Initiative (K-DOQI) guidelines. This recommendation is opinion-based and could negatively affect secondary hyperparathyroidism. Studies have suggested that a dialysate Ca of 3.0 mEq/L is a compromise between bone protection and cardiovascular risk. The aim of our study was to investigate the effect on bone metabolism parameters after increasing the dialysate Ca concentration from 2.5 to 3.0 mEq/L. The dialysate Ca concentration in our patients was increased from 2.5 to 3.0 mEq/L. Patients with hypercalcemia, normal-high Ca levels with a high Ca-Phosphorus product (Ca x P), excessively suppressed parathyroid hormone (PTH), or a past medical history of calciphylaxis were excluded. Twenty-two patients were studied over 20 weeks. Parathyroid hormone levels decreased significantly (442 +/- 254 vs. 255 +/- 226 pg/mL; p=0.000), without significant changes in serum Ca, P, and Ca x P levels at any sampling point. Better control of secondary hyperparathyroidism allowed us to decrease the paracalcitol dosage in 6 of the 12 patients who had been treated with this drug at the beginning of the study. Other potential factors involved in PTH secretion were not modified. A significant improvement in the rate of patients with 3 or more K-DOQI parameters within the target ranges (8 [36%] vs. 12 [55%]; p=0.026) was observed. In the absence of hypercalcemia or excessively suppressed PTH, an increase from 2.5 mEq to 3.0 mEq/L in dialysate Ca concentration resulted in better control of secondary hyperparathyroidism without affecting Ca, P, and Ca x P levels, thus enabling us to reduce the dosage of vitamin D metabolites.