Although topical vitamin D3 derivatives have been used in the treatment of patients with psoriasis for the past 15 years, questions remain about the indications and limitations of application. Extensive personal experience gained during the development of calcitriol (1alpha25-dihydroxyvitamin D3) is therefore reviewed. Three double-blind, vehicle-controlled trials have revealed that calcitriol 3 microg g(-1) ointment (Silkis ointment, Galderma Laboratories) has very good clinical efficacy. In a left-right comparison with vehicle ointment, complete clearance of psoriatic lesions was achieved in 48% of sites treated with calcitriol and a further 41% showed considerable or definite improvement. The clinical response to calcitriol in another study was as good as, or even better than, that achieved with betamethasone valerate 0.1% ointment. A preparation containing calcitriol 15 microg g(-1) did not show any clinical superiority to the lower dose but was associated with a higher risk of hypercalciuria, particularly when applied to extensive skin lesions. These results suggest that calcitriol 3 microg g(-1) ointment is an effective and safe treatment for chronic plaque psoriasis.