SUMMARYThe hairless mouse screening model for antipsoriatic drugs was improved by investigating the effects of critical variables on the rate of ultraviolet light‐induced epidermal DNA synthesis. The variables investigated were diurnal variation, ultraviolet light dose, time course and ambient temperature. From these studies a set of experimental conditions was developed that resulted in the lowest rate of DNA synthesis in non‐irradiated epidermis and the highest rate in irradiated epidermis, thereby significantly increasing the power of the as