The effect of cessation of erythromycin (EM) therapy against diffuse panbronchiolitis was studied. Nine cases were examined. After cessation of EM therapy, the manifestations of disease were stable in five cases, but worsened in the other four. In the former five, the period from the onset of disease until EM therapy began was relatively short; when EM therapy was stopped the manifestations of disease had almost completely disappeared and chest roentgenography revealed resolution of diffuse, small, nodular opacities without remarkable bronchiectasis. In contrast, in the latter four cases, the clinical manifestations of disease did not disappear, and chest-roentgenographic evidence of bronchiectasis was common before the cessation of EM therapy. In conclusion, EM therapy for diffuse panbronchiolitis may be stopped if the clinical manifestations of disease (especially purulent sputum) disappear, if diffuse, nodular opacities resolve almost completely and if there is no evidence of bronchiectasis.