Polymorphic light eruption is one of the few dermatological diseases in which some antioxidants have been said to be reduced in both the epidermis and the blood. This study measured the hydrosoluble antioxidant capacity in the serum of patients with polymorphic light eruption, using a commercially available kit. All patients were tested in winter, in order to avoid the influence of exposure to ultraviolet light. The results showed that a hydrosoluble antioxidant capacity was significantly decreased (by 29%) in patients with polymorphic light eruption, and b) that females (both patients and controls) has less hydrosoluble antioxidant capacity (by 27%) than males. In addition, the hydrosoluble antioxidant capacity values for females with polymorphic light eruption increased significantly with age, possibly accounting for the well-known propensity of young women to polymorphic light eruption. These last observations have not been reported previously.