BACKGROUND It has become evident that calcitriol can suppress parathyroid hormone (PTH) secretion by direct genomic actions. Intravenous calcitriol that bypasses gastrointestinal degradation might cause less degree of hypercalcemia and greater suppressive effect on PTH secretion. We investigated this PTH-suppressive effect of intravenous calcitriol in hemodialysis patients with secondary hyperparathyroidism. METHODS Calcitriol was administered at the end of each dialysis session three times a week in 20 uremic patients, for 12 weeks. RESULTS The mean dosage of calcitriol was 2.72 +/- 0.21 microgram per dialysis session. Serum intact PTH and C-PTH decreased (P < 0.05) after 6 weeks of treatment, while serum alkaline phosphatase (Alk-P) decreased 3 weeks later than PTH did. The individual maximal reduction of intact PTH, C-PTH and Alk-P were 77.80%, 67.36% and 45.98%. This PTH-suppression was dose-dependent. Despite the significant reduction of intact PTH by 58.17% after 6 weeks of treatment, no significant increase of serum calcium was found. An increase in serum calcium is not essential for this PTH-suppressive effect of calcitriol. Our observations thus provide another evidence to support the direct inhibitory effect of calcitriol on PTH secretion. Serum calcium, phosphorus, magnesium, albumin and osteocalcin levels did not change significantly. No side effect was found during treatment. CONCLUSIONS Intravenous calcitriol is effective and safe in treating hemodialysis patients with secondary hyperparathyroidism. This treatment is more important in patients who are intolerant to oral vitamin D supply and who are candidates for surgical parathyroidectomy.