Ventilatory dysfunction has become the main focus of current research in sudden infant death syndrome (SIDS). This has been correlated with structural abnormalities in the carotid body and respiratory nuclei of the brainstem. In recent studies, the denervating effect of asphyxial brainstem dysfunction on the pulmonary neuroendocrine cells, which probably function as chemoreceptors, was demonstrated and prompted the following study. The pulmonary neuroendocrine system was evaluated in 25 victims of SIDS and 20 control infants, ranging in age from 3 weeks to 7 months and 1 to 12 months, respectively. The pulmonary neuroendocrine cells were stained by the Churukian-Schenk method and the neuroendocrine cell-positive airway values expressed as a percentage of the total number of airways. The range of positive airway values for victims of SIDS was 2% to 97% with a median of 73%. In contrast, the range for the control infants was 1% to 44% with a median of 25.5%. The SIDS victims' percentage was significantly greater than the control infants' percentage (P< .0001). The number of pulmonary neuroendocrine cells in positive airway was also increased among SIDS victims compared with control infants. The altered plumonary neuroendocrine cell pattern could be attributable to either brainstem dysfunction or chronic hypoxia. These explanations are not, however, mutually exclusive of one another; in fact, it is possible that both mechanisms may be operative.