For many years attempts have been made to associate "polymorphic light eruptions," such as urticaria solaris, eczema solare, and purpura solaris with abnormalities of porphyrin metabolism. Hydroa aestivale or vesiculobullous photocutaneous lesions occur in congenital erythropoietic porphyria (Morbus Günther) and with cutaneous forms of hepatic porphyria, in all of which the urinary uroporphyrin is invariably increased and characteristic, while in the polymorphous eruptions just alluded to, the urinary porphyrin is normal. In 1953, Kosenow and Treibs1reported the case of a 12-year-old male with atypical hydroa aestivale without excessive urinary porphyrin but with elevated erythrocyte protoporphyrin (EP) and fecal protoporphyrin (FP). Although this probably represents the first recorded example of what has come to be designated as erythropoietic protoporphyria,2interpretation is somewhat complicated by the presence in the patient's serum of a porphyrin metal complex, the absorption spectrum of which corresponded with that of uroporphyrin or coproporphyrin rather