Tannic acid was used as a mordant to enhance the preservation of lung phospholipids during fixation and processing for electron microscopy. We found multilamellar bodies within alveolar septa (including type I pneumocytes, capillary endothelial cells, and interstitium) which have not been described previously and which we did not see in other tissues. The center to center spacing between lamella of these bodies was 45 A. The similarity of these structures to mixtures of phosphatidylcholine and to type II pneumocyte lamellar bodies suggest to us a function of these bodies in lung surfactant metabolism.