Management of secondary hyperparathyroidism is difficult because of the interrelationship of parathyroid hormone, calcium and phosphorus. This study was carried out to assess the efficacy of intravenous administration of alfacalcidol once weekly versus twice weekly in patients with severe hyperparathyroidism. Twenty-one hemodialysis patients with intact parathyroid hormone >88 pmol/L were divided into two groups. Eleven patients (Group 1) were given a once-weekly alfacalcidol intravenously for 12 weeks. The starting dose was 4 microg which was increased or decreased by 1 microg per week. Ten patients (Group 2) were given twice-weekly alfacalcidol intravenously for 12 weeks. The starting dose was 2 microg twice weekly which was increased or decreased by 0.5 microg/dose. The dose was increased or decreased according to serum calcium and phosphorus levels. Serum calcium, phosphorus and alkaline phosphatase levels were measured weekly and intact parathyroid hormone every 4 weeks. Intact parathyroid hormone reduced significantly (P = 0.0001) from 128.12 +/- 35.42 pmol/L to 82.93 +/- 65.20 pmol/L and from 113.74 +/- 40.83 pmol/L to 64.24 +/- 35.17 pmol/L after 4 weeks in Groups 1 and 2, respectively. After 4 weeks alkaline phosphatase declined significantly (P = 0.0001) from 146.0 +/- 57.3 IU/L to 116.0 +/- 45.6 IU/L in Group 1 and from 139.0 +/- 45.1 IU/L to 116.6 +/- 38 IU/L in Group 2. There were no significant differences in serum levels of calcium, phosphorous or their product. Interestingly, an adenoma disappeared in one patient from Group 1, and out of two adenomas, one disappeared from another patient in the same group. These results indicate that intravenous alfacalcidol once weekly is safe and effective in suppressing high parathyroid hormone in hemodialysis patients.