A patient with greatly increased erythrocyte protoporphyrin, but normal porphyrins in urine and feces, is described. The patient later developed a malignant lymphoma, and the reason why she accumulated protoporphyrin in her erythrocytes is not known. The protoporphyrin in the erythrocytes consisted of two types of protoporphyrin, free protoporphyrin (30%) and zinc protoporphyrin (70%). Upon irradiation of erythrocytes in the absence of albumin, protoporphyrin and zinc protoporphyrin, which were both bound to hemoglobin, were released. In contrast, when the irradiation was carried out in the presence of albumin, the photohemolysis was negligible, and there was release of free protoporphyrin, but not of zinc protoporphyrin, from the erythrocytes. In vivo albumin is present in the plasma and the results may help to explain why patients with erythropoietic protoporphyria (erythrocytes containing free protoporphyrin) are photosensitive, whereas patients with lead intoxication and iron deficiency (erythrocytes containing zinc protoporphyrin) are not.