This study was performed to determine the value of transbronchial biopsy (TBB) in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides and mild-to-moderate pulmonary involvement. Included in the study were 19 patients with Wegener's granulomatosis (WG) and six patients with Churg-Strauss syndrome (CSS) with evidence of active pulmonary disease but without gross parenchymal lesions accessible by radiologically guided biopsy. All of the patients had undergone staging examinations which included TBB taken from peripheral lung tissue and from any focal tracheobronchial lesions. Any suspicious lesion in the upper respiratory tract was biopsied by an otolaryngologist and the number of positive biopsies was compared with that of TBB. In the WG patients, only two out of 17 biopsies of alveolar tissue yielded histopathological findings supporting the diagnosis of WG. In five WG patients, ulcerative or exophytic airway lesions were found whose histopathologies were invariably positive. Otolaryngological examination revealed abnormal findings in 19 WG patients and biopsies from these sites yielded positive results in 13 instances. In CSS, TBB produced a diagnostically helpful histopathology in four of six cases and biopsies from the upper respiratory tract were positive in five out of six cases. We conclude that transbronchial biopsies of alveolar tissue are seldom positive in Wegener's granulomatosis patients with mild-to-moderate pulmonary disease unless they are taken from grossly abnormal lung areas. Conversely, ulcerative, exophytic or stenotic tracheobronchial lesions had a high rate of positive findings. These results further suggest that the upper rather than the lower respiratory tract should be the biopsy site of first choice in Wegener's granulomatosis. In Churg-Strauss syndrome, the upper and lower respiratory tract seem to yield a roughly equal number of positive biopsies.