The clinical features of polymorphous light eruption (PLE) are reviewed from the literature with special emphasis on the experimental reproduction of skin lesions. Our clinical experience with 180 patients is reported. In forty-three patients a newly developed UVA provocation test was performed UVA, free of sunburn radiation (50–100 J/cm²), was administered, sometimes repeatedly up to four times, to large sites of previously involved skin. With this technic the reproduction of PLE lesions under laboratory conditions was possible in 90% of this group of forty-three patients. The diagnosis was substantiated by microscopic examination of genuine and experimentally induced lesions. Characteristic histologic features of PLE are described Phototesting with large doses of UVA aids in confirming the diagnosis of PLE Hitherto, this diagnosis depended often on exclusion of other dermatoses Eusolex 8021, a UVA-effective sunscreen, blocked eruptions of PLE lesions under laboratory conditions. An effective means of treatment is offered by PUVA therapy.