Seven patients on chronic hemodialysis were given alphacalcidol (1 alpha-OH-vitamin D3) intravenously in a pilot study during 3 months. Before treatment all patients had serum calcium values within the normal range, but elevated levels of parathyroid hormone (PTH). When serum calcium was raised above the normal range by treatment with alphacalcidol, all patients displayed marked suppression of PTH levels with a mean reduction of 40 +/- 20% (SD; p less than 0.01). When the dose of alphacalcidol was reduced so that the serum calcium values were kept at the upper limit of the normal range, a partial return towards pretreatment values of PTH was seen but the levels were still lowered (p less than 0.05). Thus, intravenous administration of the vitamin D compound appeared to be useful for the management of secondary hyperparathyroidism in patients on dialysis. A direct effect of alphacalcidol on the parathyroid glands could, however, not be distinguished from the calcemic action.