The authors studied by electron microscope, the sun-exposed skin of the back of the hand from three heavily hemodialysed patients with a porphyria cutanea tarda-like bullous skin disease. The vascular impairment, like that of PCT, closely resembles that seen during medicamentous phototoxic processes. The connective tissue is infiltrated by large granulo-filamentous masses and the fibroblasts are secretory in appearance. At the dermal-epidermal junction, the abnormalities are important, with a diffuse infiltration of the upper dermis by a hyalin substance, probably resulting in a collagen degeneration and cellular necrosis. The aetiological factors are uncertain, as no common medicamentous factor appeared in our patients, and as the plasticizers used in the hemodialysis tubes probably played no part.