We analyzed 36 open lung biopsy specimens from patients with chronic pigeon breeder's disease (PBD) to assess bronchiolar involvement and its relationship to the parenchymal pathologic abnormalities. Likewise, 21 biopsy specimens obtained from patients with usual interstitial pneumonia (UIP) were also examined. The bronchiolar abnormalities were scored by the method of Wright et al using a panel of photographs. In addition, the severity of lung fibrosis was evaluated in all samples and expressed as percentage in multiples of ten. A variable degree of epithelial cell metaplasia, bronchiolar inflammation and fibrosis, smooth muscle hypertrophy, extrinsic small airways narrowing, and intraluminal macrophages was observed in both diseases. Occasionally, hyperplasia of lymphoid follicles was also present. Bronchiolar changes were proportional in type and severity to the parenchymal damage. Spearman's nonparametric correlation between fibrosis in parenchyma and fibrosis in membranous bronchiole for the complete group (including patients with UIP and with PBD) showed a moderate but significant association (R = 0.51; p < 0.01). A significant association was also demonstrated when the score for bronchiolar fibrosis and inflammation was evaluated in relation to lung fibrosis divided in high degree (> 50%) and low degree (< 50%), respectively. In the case of patients with PBD, the correlation between bronchiolar and parenchymatous fibrosis was of 0.33 (p < 0.05). In general, bronchiolar fibrosis was less severe and inflammation more severe in PBD lungs compared with patients with UIP. Fibrosis in membranous bronchioles correlated with increased mortality in the complete group of patients, but the impact on mortality disappeared after correcting for overall fibrosis in the biopsy sample. Our findings demonstrate that a spectrum of bronchiolar lesions is usually observed in chronic PBD lungs, although the predominant pattern is similar to that found in the surrounding parenchyma, suggesting that the damage occurs in parallel.