The invention provides 25-hydroxyvitamin D for use in the treatment of hyperparathyroidism by controlled release. The 25-hydroxyvitamin D is administered by intravenous delivery, especially in dosage amounts of from 1 to 100 µg per day. The 25-hydroxyvitamin D may be (a) 25-hydroxyvitamin D2 or (b) 25-hydroxyvitamin D3 or (c) a combination of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3.