Exfoliated cells of the human buccal mucosa were studied in 35 adults. All cells showed signs of necrosis: condensation of nuclear chromatin, dilated mitochondria with flocculent densities, dilation of endoplasmic reticulum, ribosomes detached from the endoplasmic membranes, aggregates of degenerated organelles in the cytoplasm, and discontinuity of nuclear and plasma membranes. Desmosomes were preserved in cells exfoliated in groups, but in single cells the former sites of desmosomes were only occasionally identified. The cells contained filaments about 150 A in diameter, often arranged in bundles around aggregates of degenerated organelles. Ruthenium red stained the glycocalyx of the epithelial cells and the capsule of accompanying bacteria. The glycocalyx did not appear to contribute to binding the bacteria to cell surfaces. The findings are discussed in the light of recent studies on cell necrosis, and culminate in a hypothesis to explain exfoliation of cells of the oral epithelium.