It is well known that erythromycin (EM) therapy is effective on chronic lower respiratory tract disease, including diffuse panbronchiolitis (DPB). In this study we investigated the relationship between clinical findings and neutrophil chemotactic activity (NCA) in bronchoalveolar lavage fluid (BALF) in patients with DPB receiving orally EM therapy. The NCA in post-EM therapy BALF was significantly reduced (p less than 0.001) compared with that in BALF before EM therapy (30.17 +/- 7.84% vs 53.05 +/- 10.65%). On the respiratory function before and after EM therapy, DPB patients (20 cases) showed significant improvement of %VC, FEV1.0, RV/TLC (p less than 0.001, each) and V25 (p less than 0.05). And on the post-EM therapy blood gas, PaO2 and AaDO2 level were confirmed to be significantly improved (p less than 0.001). In addition, we examined the correlation between the improvement ratio of clinical finding and the reduction of NCA in BALF after EM therapy in 10 patients with DPB. We found the significant correlation between the improvement ratio of PaO2 and the reduction NCA in BALF of those patients (p less than 0.05). There were no significant relationships between the improvement ratio in other parameters as stated above and the reduction of NCA in BALF. These findings indicate that EM restrains the NCA in BALF of patients with DPB and impairs the accumulation of neutrophils in respiratory tract, ultimately contributes to the improvement of clinical symptoms such as sputum and clinical findings such as PaO2 in patients with DPB.