Autoradiographs were prepared from lungs of a newborn Syrian golden hamster exposed continuously to [3H]thymidine throughout the final 4.5 days of gestation. Silver grains were counted over nuclei of 1,145 nonendocrine airway epithelial cells adjacent to 28 mature neuroepithelial bodies (NEBs). Generally, accumulated label was greater in cells nearer a NEB than in those further away. Diminution of label with increasing distance from the closet NEB was confirmed statistically. In 24 of 28 instances, both rank-order correlation and linear regression were significant (P less than 0.001-0.05); in two others, only one test was significant; in another two, neither test was significant. The pattern was consistent and widespread. Rank-order correlations and linear regressions were significant (P less than 0.001) in populations pooled separately from left lung, right upper, and right lower lobes, and the three regression lines were superimposable. Confirmation was obtained in another animal by labeling S-phase cells with a 2-h transplacental pulse of bromodeoxyuridine (BrdU) on fetal day 15. Of 322 BrdU-positive cells counted in 270,204 microns 2 of bronchial epithelium, 174 (54%) lay within 20 microns of a neuroepithelial body. This concentration of dividing cells was significant by chi-square test: chi 2[1] = 101.62; P less than 0.001. We conclude that established NEBs promote growth of the developing airway by stimulating proliferation of local endoderm. A few daughter cells may enter NEBs; most move away to join the expanding nonendocrine airway lining.