Calcitriol therapy is effective in the treatment of secondary hyperparathyroidism both during intravenous and oral administration, but there are doubts about the length of therapy and the duration of results. There are conflicting reports about results in size and activity of enlarged glands studied by ultrasound and double-tracer-subtraction-scintigraphy (DTSS). In 12 patients, 1 microgram of calcitriol was administered three times a week, intravenously and orally in alternate modes, for 46 weeks (therapy period) and orally for 46 weeks (follow-up period). During therapy, parathyroid hormone levels decreased in all patients, and in eight decreased by about 50% and were maintained at low levels during follow-up in five patients. Nine enlarged glands were detected by ultrasonography at the start of the study, and four hotspots were detected by DTSS; ultrasonography and DTSS were repeated at the end of the therapy and at the end of the follow-up: ultrasonography did not yield any significant variation in size, while one hot spot disappeared on DTSS. Basing their judgment on the lower cost of oral rather than intravenous administration, and on the good results of oral therapy, the authors stress the advisability of taking into account clinical and financial considerations before choosing the route of administration.