Alveolar proteinosis (AP) and postobstructive or endogenous lipid pneumonia (ELP) are two distinct morphologic types of phospholipid accumulation in the lung. In ELP, ultrastructurally amorphous fat accumulates in the cytoplasm of alveolar macrophages. In AP, lamellar surfactant bodies with an electron microscopic complex structure are stored within alveolar lumina. In contrast to ELP, AP has not been associated with bronchial obstruction. One case of postobstructive AP occurred distal to a central carcinoid tumor, and two cases of combined AP and ELP occurred next to a squamous cell carcinoma that obstructed a lobar bronchus. Results of histologic and ultrastructural studies were determined with regard to new insights into the physiology and biochemistry of pulmonary lipids. It was concluded that the morphology of accumulated fat in obstructed lung tissue may depend on local oxygen and carbon dioxide tensions.