Diffuse panbronchiolitis (DPB) and asthma are obstructive airway diseases, the former being characterized by Th1-type and the latter by Th2type airway inflammation. Differential diagnosis is often a problem, but coexistence has rarely been reported. A 76-year-old man with asthma was admitted to our hospital because of one-month history of dyspnoea on exertion with bilateral diffuse granular shadows. He also had a history of chronic sinusitis. Auscultation of the lungs showed coarse crackles and wheezes. Laboratory data revealed an elevated total serum immunoglobulin E and a high titre of cold agglutinin. Bronchoscopic evaluations of the shadows revealed compatible pathological findings in both DPB and asthma. Low-dose macrolide caused a prompt reduction of symptoms, along with improvements in radiographic findings and pulmonary functions, whereas the eosinophilic airway inflammation transiently worsened. When DPB and asthma coexist, the balance of Th1/Th2 immune response may be reciprocally altered by therapeutic intervention.