The aim of this prospective and randomized study was to compare the efficacy, side effects, and costs of 'pulse oral' versus intravenous calcitriol in the treatment of secondary hyperparathyroidism in hemodialysis (HD) patients. A total of 20 patients were randomized to receive over a 4-month period pulse orally administered calcitriol (pulse oral group; n = 10) or intravenous calcitriol (intravenous group; n = 10). All patients used standard dialysate calcium (1.75 mmol/l) throughout the study period. In accordance with the study design calcium dialysate concentrations were reduced when this was necessary to avoid hypercalcemic crises. The patients were stratified into two subgroups according to their initial serum PTH levels: patients with mild or moderate degree of hyperparathyroidism (17 patients) and patients with severe hyperparathyroidism (3 patients). Intravenous and pulse oral cacitriol did not significantly reduce serum PTH concentrations in patients with severe hyperparathyroidism (1,157 +/- 156 vs. 807 +/- 228 pg/ml [corrected], p = 0.09). Intermittent calcitriol, administered by intravenous or oral route, significantly reduced serum PTH levels (326 +/- 119 vs. 109 +/- 79 pg/ml [corrected], p = 0.0001) in patients with mild or moderate hyperparathyroidism. In patients with mild or moderate hyperparathyroidism, intravenous calcitriol significantly reduced PTH concentrations at the end of the 1st month, before the increase of serum ionized calcium levels, whereas 'pulse oral' calcitriol significantly suppressed parathyroid activity at the end of the 2nd month. Calcium dialysate concentration was reduced in 9 out of 10 (90%) patients of the pulse oral group and in all patients (10/10) of intravenous group. The incidence of hypercalcemic crises was 24% (39/160) in the pulse oral group and 14% (27/160) in the intravenous group. Analysis of costs showed that intravenous calcitriol was more expensive compared to pulse oral calcitriol. These data indicate that intermittent intensive calcitriol therapy, regardless of the route of administration, is effective in suppressing parathyroid activity in HD patients with mild or moderate hyperparathyroidism. In contrast, intermittent calcitriol therapy has a limited ability to achieve sustained serum PTH reductions in HD patients with severe hyperparathyroidism. Intravenous calcitriol was more expensive than pulse oral calcitriol, and we recommend the use of pulse oral calcitriol in HD patients with mild or moderate secondary hyperparathyroidism.