Tacalcitol is a vitamin D analogue which ahs been developed for the therapy of psoriasis vulgaris. The treatment with a twice daily application of 2 micrograms/g ointment is efficacious and safe in Japanese patients. The objective of this randomized, placebo-controlled, intraindividual right-left comparison was to investigate the efficacy and safety of 8 weeks' therapy with a once daily application of a 4 micrograms/g tacalcitol ointment in Caucasian psoriatics. The data on 122 male and female patients were analysed. The score sum of erythema, infiltration and desquamation was influenced significantly more by tacalcitol ointment than by placebo (P < 0.0001) at every control point, starting from week 2. With regard to the individual symptoms of desquamation, infiltration and erythema, the treatment with tacalcitol was also superior to placebo treatment beginning at week 2. Qualitatively, the same results were obtained with the preference assessment of both treated body sides and also the global assessments of efficacy and benefit. Symptoms of local skin irritation which may be related to the active compound or the ointment base were reported by 12.3% of patients. In only one patient, irritation required discontinuation of tacalcitol treatment. Laboratory criteria, including serum calcium, serum phosphate and serum levels of calcitonin, parathormone, 1 alpha, 24-dihydroxyvitamin D3 and 25-hydroxyvitamin D3, did not reveal any changes of clinical relevance during or after treatment. Furthermore, the global assessment of tolerance was good or very good in more than 90% of cases. The results of this study demonstrate that the once daily application of a 4 micrograms/g tacalcitol ointment is an efficacious therapy for psoriasis vulgaris in Caucasian patients, and that its tolerance is good, wherever the lesion is located, including on the face.