After a washout period of 28±3 days under 0.5 µg alfacalcidol /day, the patients will follow the second period of treatment. The study will end with a final period of 28±3 days under 0.5 µg alfacalcidol /day. Patients will ambulatory monitor serum calcium, sodium, potassium, and creatinine levels at days 15 of run in and run out periods and at day 7 and day 28 of each treatment period.