This study compared the effects of oral and intravenous calcitriol on serum biochemistry parameters and levels of bone-resorptive cytokines in haemodialysis patients. Patients were randomized to receive oral (n = 18) or intravenous (n = 16) calcitriol treatment for 6 months. Serum levels of total calcium, ionized calcium, intact parathyroid hormone (iPTH), magnesium, alkaline phosphatase, tumour necrosis factor-et (TNF-alpha), interleukin (IL)-1 and IL-6 were measured at baseline and after 3 and 6 months of treatment. After treatment, serum levels of iPTH, total calcium, ionized calcium, TNF-alpha, IL-1 and IL-6 were not significantly different from baseline. The intravenous calcitriol treatment group showed significant decreases in levels of iPTH, TNF-alpha, IL-1 and IL-6 and a significant increase in total calcium level after 3 and 6 months. There was no significant change in serum ionized calcium levels. Significantly decreased serum alkaline phosphatase and magnesium levels were found in both treatment groups after 3 and 6 months. In conclusion, intravenous calcitriol treatment has a significant depressive effect on iPTH and bone-resorptive cytokines in patients undergoing haemodialysis.