Corticosteroids and vitamin D3 analogues inhibit proliferation, enhance normal keratinisation and interfere with cutaneous inflammation in in vitro systems. Both treatments are effective in psoriasis, although several reports suggest that vitamin D3 is less effective in reducing the inflammatory changes compared to its potent effect on keratinocyte growth and differentiation. The aim of the present study was to compare and contrast the effects of the vitamin D3 analogue calcipotriol, clobetasol-17-propionate and a placebo on immunohistochemical markers for epidermal growth, keratinisation and inflammation induced by a standardised single challenge with ultraviolet B (UVB) radiation in normal human skin. Clobetasol proved to inhibit UVB-induced proliferation of epidermal cells, tenascin induction, keratin 16 induction and the accumulation of T lymphocytes and CD la-positive cells. Epidermal thinning due to clobetasol was also observed. No effect of clobetasol was shown on the enhanced terminal differentiation following UVB challenge. In contrast, calcipotriol reduced the member of transglutaminase-positive cells following UVB challenge but increased the thickness of the epidermis without a significant effect on other markers for keratinisation, epidermal proliferation and inflammation. The present study reconfirms the potent effect of topical corticosteroids on various aspects of UVB-challenged skin. In contrast, calcipotriol interfered especially with one differentiation pathway (transglutaminase) without modulation of other UVB-induced changes.