Tacalcitol is a vitamin D3 analogue which is available in Japan as a 2 micrograms/g ointment for twice daily application and in Western markets as a 4 micrograms/g ointment for once daily application. Tacalcitol inhibits proliferation, and induces the differentiation, of keratinocytes. In addition, it appears to modulate inflammatory and immunological mediators in the skin which may be involved in the aetiology of psoriasis. No significant systemic drug absorption occurs after application of tacalcitol to the skin. Results of clinical trials indicate that topical tacalcitol is effective in the management of stable plaque psoriasis (and possibly pustular forms of the disease), and has a similar efficacy to topical betamethasone valerate in this setting. Application of tacalcitol ointment 4 micrograms/g once daily for up to 8 weeks did not cause hypercalcaemia or hypercalciuria. Mild local skin irritation has been reported in a variable proportion of patients (< or = 12%).