The clinical and pathologic features of diffuse panbronchiolitis (DPB) have been well reported to date, although its pathogenesis remains unknown. In the present study, we performed bronchoalveolar lavage (BAL) on three patients with biopsy specimen-proven DPB and eight patients with highly probable DPB (six women and five men; one smoker and ten nonsmokers), nine patients with chronic bronchitis (all men, five smokers and four nonsmokers), and nine normal control subjects (six women and three men, all nonsmokers) to clarify the cell populations in the lower respiratory tract. Neutrophils comprised 55.3 +/- 24.4 percent of recovered cells by BAL in DPB patients but only 6.6 +/- 6.4 percent in chronic bronchitis patients, and 1.8 +/- 1.5 percent in normal control subjects (p less than 0.001, all comparisons). The DPB patients also exhibited a decreased percentage of alveolar macrophages (34.9 +/- 23.5 percent) compared with chronic bronchitis patients and normal control subjects (p less than 0.001, all comparisons). The percentage of lymphocytes of the recovered lavage cells in DPB patients did not differ from that in chronic bronchitis patients and normal control subjects. These results indicate that neutrophils play an important role in the pathogenesis of DPB. They also suggest that neutrophilia of BAL-recovered fluid is a common finding in diseases associated with bronchiolar inflammation despite some clinical and pathophysiologic differences.