The light, polarization and electron microscopic changes in the liver of four cases of erythropoietic protoporphyria (EPP) are described. In one of these cases liver involvement resulted in death, whereas in the other three there were no symptoms of referable to hepatic disease. In two cases hepatic pigment was readily visible on light and polarization microscopy and corresponded to characteristic crystalline aggregates seen ultrastructurally. Pronounced micronodular cirrhosis and cholestasis were present in the fatal case, while in the other only mild periportal fibrosis and mononuclear inflammatory cell infiltrate occurred. The third and fourth cases showed no evidence of hepatic involvement on light microscopy. Electron microscopy, however, revealed characteristic crystal-containing vacuoles indicative of protoporphyrin deposition. The need for early detection of the hepatic lesion is emphasized.