To evaluate the effects of roxithromycin in patients with chronic lower respiratory tract disease including diffuse panbronchiolitis, we studied lymphocyte function-associated antigen-1 (LFA-1) and Mac-1, neutrophil adhesion molecules, using peripheral neutrophils from healthy volunteers and from patients with chronic lower respiratory tract disease. The number of Mac-1 expressed on neutrophils of the patients was significantly greater (0.68 ± 0.16) than in the healthy subjects (0.45 ± 0.14), while the number of LFA-1 expressed on neutrophils of the patients was nearly similar to that in the healthy volunteers (0.95 ± 0.10 vs. 0.89 ± 0.11). The neutrophil numbers in bronchoalveolar lavage fluid and the number of Mac-1 expressed on peripheral neutrophils significantly decreased in all patients who responded clinically to a low dose of roxithromycin for a long period of time (56.0 ± 25.2 vs. 22.7 ± 19.7%, p < 0.05 and 0.70 ± 0.16 vs. 0.59 ± 0.08, p < 0.05, respectively), whereas roxithromycin had no effect on the quantitative expression of LFA-1 (0.96 ± 0.14 to 1.00 ± 0.09, not significant) in all r