Neutral endopeptidase (NEP) may regulate peptide-induced inflammation in the upper respiratory tract. NEP mRNA was detected by Northern blotting in poly(A)+ mRNA prepared from human turbinates. NEP mRNA bands were detected at 3.9 and 1.8 kb. In situ hybridization identified NEP mRNA in epithelial cells, serous cells of submucosal glands, and vessel walls. The vacuoles of goblet and mucous cells were not stained, but it is likely that the cytoplasm of these cells contained some NEP mRNA. Radioactive in situ hybridization with 35S-UTP appeared to be more sensitive than nonradioactive in situ hybridization with biotin-UTP and immunogold detection. The NEP mRNA-containing cells identified by in situ hybridization were the same as those identified by immunohistochemistry to contain immunoreactive NEP. These NEP-containing cells have been previously shown to possess peptide receptors. This is consistent with the hypothesis that NEP on cells bearing peptide receptors may regulate neuropeptide-induced inflammation in human nasal mucosa.