A standardized hepatological investigation was performed in 9 unselected patients with erythropoietic protoporphyria (EPP). The aim of this study was to detect early liver involvement due to EPP and to determine the significance of several diagnostic procedures. Scintigraphy revealed slight enlargement of liver and spleen in all cases. Light microscopic examination of liver tissue in 7 patients showed protoporphyrin deposition in 4 and signs of fibrosis in 3 cases. Cirrhosis was not found. Electron microscopical examination (EM) of all 7 cases was negative and needle-shaped crystals were not found. Therefore we regard EM of little diagnostic value in the detection of early liver involvement. The literature on fatal and asymptomatic cases of liver involvement in EPP is discussed with emphasis on possible predictive and provocative factors. A proposal for EPP patients intending to reduce possible risk factors is made.