Background: The vitamin D3 derivative calcipotriol (Daivonex®) is an efficient topical treatment of psoriasis. When applied at a dose of about 25 g/week over a mean body surface of 16%, it is not associated with any detectable change in calcium metabolism. Objective: Our purposes were (i) to analyze the effects of calcipotriol on various parameters of calcium metabolism when applied on a large body surface and (ii) to evaluate the usefulness of an oral calcium tolerance test in monitoring psoriatic patients under topical calcipotriol. Methods: In group 1, 10 patients with psoriasis affecting 67.0 ± 2.7% of total body surface (range 55–80%) were treated with calcipotriol for 6.5 weeks (mean 383 g/month). In group 2, 19 patients with psoriasis involving 15% of body surface were treated with calcipotriol for 9 weeks (mean 105 g/month). In group 3, 7 patients without topical calcipotriol for at least 1 week were given 1.5 μg of oral calcitriol for 7 days. An extended survey of blood and urinary parameters of calcium metabolism was performed before and after 45 days of treatment (group 1). Since one of the actions of vitamin D is to stimulate intestinal calcium absorption, an oral calcium-loading test (groups 1, 2 and 3) was done in order to detect more subtle changes possibly induced by calcipotriol. Results: We did not detect any significant change in various parameters of calcium metabolism in group 1 (large body surface treated) patients. The urinary calcium responses to the oral calcium load were identical to controls in both group 1 (large body surface treated) and group 2 (limited body surface treated), whereas in group 3 (oral calcitriol therapy) an increased urinary calcium response to the calcium load was identified. Conclusions: No significant changes in calcium metabolism were detectable when calcipotriol was administered once a day over a large body surface with doses up to 100 g/week. The oral calcium tolerance test appears to be a cheap, simple and sensitive test to monitor patients exposed to high doses of calcipotriol as it detects increased intestinal calcium absorption induced by 1.5 μg of oral calci