We have obtained endobronchial biopsies (EBB), bronchoalveolar lavage (BAL), and transbronchial biopsies (TBB) in 17 stable lung transplant recipients (sLTR), 8 subjects with physiologic evidence of chronic rejection (BOS), and 9 normal subjects. A striking finding was the marked neutrophilia in BAL samples from patients with BOS, in the carefully screened absence of infection. A statistically higher neutrophil count was also present in the sLTR group relative to the normal group. Median BAL neutrophil count in BOS was 100 x 10(3)/ml, range 13-1,661 10(3)/ml (p < 0.001 relative to normal subjects and sLTR). Median BAL neutrophil count in sLTR was 7 x 10(3)/ml, range 1-81 10(3)/ml (p < 0.01 relative to normal subjects). Normal subjects had a median BAL neutrophil count of 3 x 10(3)/ml, range 1-7 10(3)/ml. There was evidence of a predominance of CD8 lymphocytes in BAL from sLTR and BOS with a lower CD4/CD8 ratio in both compared to normal subjects (p < 0.05). EBB mononuclear cell counts, class II major histocompatibility complex expression, and T-cell activation markers were normal in BOS, in contrast to the sLTR group. Our data may be consistent with BOS, representing a relative resolution of an active mononuclear cell chronic inflammation, perhaps at the expense of airway fibrosis. The relevance of the BAL neutrophilia and its role in BOS pathogenesis need further longitudinal investigation.