The presence and distribution of neuropeptide-containing nerves within endobronchial biopsies has been investigated in symptomatic asthmatics (n = 17) and in asymptomatic nonasthmatic control subjects (n = 17). Biopsies from large airways, obtained under local anesthesia by flexible fiberoptic bronchoscopy, were processed immediately and analyzed for nerves using specific indirect immunofluorescence with antisera to the neural marker protein gene product 9.5 (PGP 9.5) and the neuropeptides vasoactive intestinal peptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP), and neuropeptide tyrosine (NPY). PGP 9.5-positive nerves were present in all the biopsies from both subject groups, being identified in relationship to epithelium, glands, smooth muscle, and blood vessels. VIP- and NPY-immunoreactive nerves were equally present in the biopsies of both asthmatic and nonasthmatic subjects, being localized to smooth muscle and glands. Using well-substantiated antibodies, no nerves immunofluorescent for SP or CGRP were identified in any of the biopsies of the subjects. In the asthmatic patients, there were no significant correlations between the PGP 9.5, VIP, or NPY immunofluorescence scores and the resting spirometric values (FEV1) or the level of nonspecific bronchial responsiveness, as assessed by the provocative concentration of methacholine required to produce a 20% fall in FEV1. To verify the single biopsy findings, two further studies were undertaken, one in which biopsies were stained from two airway sites (proximal and distal) and a second in which the findings in carinal specimens obtained using biopsy forceps from freshly resected lung tissue were compared with those in a surrounding area of tissue.(ABSTRACT TRUNCATED AT 250 WORDS)