Histochemical and ultrastructural examinations were performed on neuroepithelial bodies (N. E. B.) in the lung of the mouse and rat. The N. E. B. were identified as specialized groups of pale, columnar cells. They were located throughout the intrapulmonary airway. These cells displayed some special cytochemical properties also seen in the APUD (Amine Precursors Uptake and Decarboxylation) endocrine system, such as cytoplasmic argyrophilia and the capability of selective uptake of amine precursors. Ultrastructrally the N. E. B. were composed of a kind of granulated cell which had concentrations of specific cored vesicles in the basal cytoplasm. It seemed likely that the cells released the contents of the cored vesicles into the extracellular space by exocytosis. These cells made extensive and intimate contact with the mitochondria-rich nerve terminals which occurred mainly at the level of the supranuclear portions of the granulated cells. In this contact area, the membrane of the nerve terminals were apposed to that of the granulated cells with a consistent gap of about 20 nm. Among these membrane appositions, some membrane thickenings were observed in which cored vesicles were closely associated in the granulated cell cytoplasm. From these observations, it was conceived that the lung N. E. B. function both as receptor and endocrine organs and that their specific cored vesicles may have an intimate correlation with these dual functions.