Several open studies with active forms of vitamin D3 have been reported to be effective in the treatment of psoriasis. We report a double-blind study of 1 alpha,25-dihydroxycholecalciferol in psoriasis using 0.5 microgram of active substance applied topically twice daily. In contrast to previous studies, the present investigation does not provide evidence of clinical efficacy for the drug at that dosage and with the vehicle that was used.