The number and volume of pulmonary neuroepithelial bodies (NEBs) of 1- and 4-week-old hamsters were estimated using unbiased stereological principles and systematic sampling techniques. For comparative purposes, volume estimations were also made in the carotid body, the parathyroid gland, and the adrenal medulla. A significant decrease was found in the total number of NEBs, immunoreactive for CGRP, between 1 and 4 weeks. Individual as well as cumulative NEB volume also decreased significantly. The cumulative NEB volume in 1-week-old hamsters was in the same range as the volumes of the carotids and parathyroids in the same animals. The postnatal decrease of the NEB number suggests that the NEBs are of primary potential importance in the neonatal stage, when they may complement the chemoreceptor function of the carotid bodies, which are relatively inactive at birth. Since the cumulative NEB volume (at least at the age of 1 week) is equal to that of the carotid bodies and the parathyroids, their physiological function may be of similar importance.