Epilithic detritus is recognized as a rich and potentially useful form of detrital material in aquatic habitats. It forms an adherent cover to the light-shaded, under-sides of submerged stones. Compared with other aquatic detrital materials it was found to be rich in organic material, protein and total potential energy content. It probably represents a primary seral stage in community succession which is prevented from maturing further by the absence of light. The potential usefulness of epilithic detritus, as food to aquatic detrivores, is discussed.