A prospective analysis of bronchoalveolar lavage (BAL) in 13 patients with Wegener's granulomatosis (WG), 20 disease control subjects with idiopathic pulmonary fibrosis (IPF), and 24 normal control subjects was conducted to (1) evaluate the quality of the alveolar inflammatory response associated with active WG; (2) determine whether antineutrophil cytoplasmic antibody (ANCA) is present in alveolar fluid and produced in the lungs of patients with WG; and (3) determine whether inhaled particles or infectious agents may play an etiologic role in WG. BAL in untreated active WG had a marked increase in neutrophils (mean = 42% of total WBC count), and usually in eosinophils (mean = 4%) compared with that in normal control subjects (1.6% neutrophils, 0% eosinophils), and untreated WG in remission (5.9% neutrophils, 0% eosinophils). Disease control subjects with IPF, a process known to be associated with neutrophilic alveolitis, had an increased population of neutrophils (15.4%) and eosinophils (2.7%) in BAL. Leukocyte remnants, as well as intact leukocytes, could be identified within BAL macrophages in the patients with WG and IPF, and rarely in the normal control subjects. Normal subjects and control patients with IPF were all negative for ANCA in serum, whereas ANCA was found in serum and BAL in all patients with active WG who had generalized disease. Protein analysis of BAL revealed a disproportionate increase in the IgG to albumin ration compared with serum values (IgG index) in patients with active untreated disease. The increase in the IgG index suggests that IgG with ANCA reactivity is produced by pulmonary lymphoid tissue. An infectious agent in BAL was not identified by any of the techniques applied in this study.(ABSTRACT TRUNCATED AT 250 WORDS)