In neonatal dogs, neuroepithelial bodies (NEB) are located in the distal lung. They consist of closely packed and granulated epithelial cells showing a positive immune reaction to serotonin and carrying well-developed apical microvilli. They make close contact with capillaries and form morphologically afferent synaptic junctions with intracorpuscular nerve endings. Since most nerve endings degenerate after hilar lung denervation, they are carried by extrinsic, most likely vagal, sensory nerve fibers. We conclude that pulmonary NEB probably are receptor organs, sampling the inspired air and secreting bioactive substances. These might have a local vaso- or bronchoactive regulatory effect, or could be carried to other body parts via the blood vessels. In addition, NEB might induce integrative reflexes via the central nervous system. The NEB intracorpuscular nerve endings also show spontaneous degeneration. This, in addition to the scarcity of NEB in the distal lungs of adult dogs, strongly suggests that the pulmonary NEB are particularly important during the perinatal period of life.