For psoriasis therapy, topical derivatives of vitamin D3 represent a versatile option: they can be used either alone or in combination with other agents such as topical corticosteroids. In this two-phase parallel-group study, the naturally occurring vitamin D3 analogue, calcitriol, was compared with the vitamin D analogue calcipotriol in 125 patients with chronic plaque-type psoriasis. The proposed treatment regimen was an initial bitherapy for 2 or 4 weeks, with clobetasol propionate 0.05% cream, a super potent topical corticosteroid applied in the morning and either calcitriol 3 mug/g ointment or calcipotriol 50 mug/g ointment applied in the evening, followed by monotherapy with either calcitriol or calcipotriol applied twice daily until endpoint week 12. Efficacy evaluations (global assessment of improvement, PASI and body surface area (BSA) affected) showed no significant differences between the two regimen groups at the primary endpoints (week 2 and week 12) or at any interim points. At week 2 the investigator's global assessment showed clinical success (psoriasis markedly improved, almost clear or clear) for more than 50% of the patients in both groups and for 48 (79%) and 56 (88%) patients, respectively in the calcitriol and calcipotriol regimen group at week 12. Least-square means analysis of PASI indicated the calcitriol regimen to be equivalent to the calcipotriol regimen. There were no significant differences between the two groups with regards to cutaneous safety or to incidence of adverse events. The present study shows that for the treatment of mild to moderate plaque psoriasis calcitriol 3 mug/g ointment can provide a safe and effective alternative to calcipotriol 50 mug/g ointment while being administered within a regimen based on a bitherapy with corticosteroids followed by a vitamin D3 maintenance monotherapy.