We have tried Allopurinol in the treatment of psoriasis, without having any knowledge of previous publications in this respect. The antigouty drug, which acts inhibiting the xanthine oxidase has proved excellent in 50%, good in 34% and moderate in 16% of the cases treated, independent of the oldness of the process. This study constitutes a new step in the metabolic pathogenesis of psoriasis which has already been the motive of other investigatory works by the authors.