Mouse gallbladder epithelium was studied in the electron microscope after glutaraldehyde and osmium tetroxide fixation and Epon embedding. Special attention was paid to dense cytoplasmic bodies. Heterogeneous dense bodies with osmiophilic and loose granular components were identified. Many of these bodies consisted of lamellated osmiophilic structures, similar to the phospholipid bodies of the large alveolar (type II) cells of the mammalian lung. The dense bodies containing the lamellar structures were membrane-limited and 0.5-1.0 mum in diameter. They were located in the supranuclear cytoplasma and were often closely associated with the Golgi apparatus. Acid phosphatase activity was demonstrated within these bodies and in some of the Golgi vacuoles. The contents were disposed in concentric lamellar osmiophilic structures, sometimes appearing as scroll-like configurations. These morphological findings were interpreted as indication of these presence of phosphlipid absorbed from the gallbladder lumen and stored in phagosomes in the central cytoplasm of the gallbladder epithelial cells.