The purpose of this study was to determine whether neutral endopeptidase (NEP; EC3.4.24.11) is decreased in the uvula epithelium of patients with obstructive sleep apnea (OSA). Tissues were obtained by uvulopharyngopalatoplasty in seven patients with moderate OSA and by autopsy in five individuals not known to have OSA. Using antisera to human NEP and immunoperoxidase staining, we found that NEP was localized in uvula epithelial cells of both patients with OSA and controls. However, there was a significant decrease in the number of epithelial cells staining for NEP in patients with OSA relative to controls (67 +/- 10 cells versus 261 +/- 33 cells, in 5 randomly selected high-power microscopic fields, respectively; mean +/- SEM; p < .05). The intensity of staining for NEP was similar in both groups. We conclude that immunoreactive NEP is significantly decreased in the uvula epithelium of patients with OSA.