The fine structure of the retinal pigment epithelium (RPE) of the barn owl (Tyto alba) is described. In general it resembles that of the retinal pigment epithelium of other vertebrate animals and a high content of myeloid bodies, lipid droplets, electron dense cytosomes, and especially phagosomes is observed. The latter show different structural specializations which include membranes, tubules, filaments, granules, vesicles, and crystalloid patterns. The central part of the retina often contains a peculiar inclusion body which is separated from the cytoplasm by one or two distinct membranes and is composed of a regularly arranged tubular network which forms a three-dimensional honeycomb structure. The tubules in part are in continuation with randomly oriented and densly packed tubules and stacks of discs consisting of paired lamellae. Similar formations within secretory cells of a gland (dendritic organ) and the taste buds of catfish are discussed.