Abstract Ultrastructural and autometallographic investigations of the midgut of experimentally intoxicated centipedes, Lithobius forficatus, have been performed to investigate the functional role of the epithelial cells in the detoxification of heavy metals. Ultrastructural study demonstrated that nonessential metals such as cadmium and lead may cause intracellular changes, i.e., appearance of electron-dense granules with a spongelike aspect and increase in the number and the size of concentrically structured granules. The autometallographic procedure demonstrated that both types of granules are the main organelles of the midgut to accumulate heavy metals. The permanent storage of metals in granules is a mechanism used by centipedes to reduce the toxic effects of heavy metals assimilated in excess. Consequently, midgut epithelium works as an efficient barrier to prevent excesses of certain metals in the internal environment.