PURPOSE: To determine evaluate the clinical effectiveness of low-dose erythromycin (EM) therapy in patients with diffuse panbronchiolitis (DPB), and to correlate the pulmonary function testing (PFT) changes seen at serial high-resolution CT (HRCT) withthe results of post-treatment. MATERIALS AND METHODS: We retrospectively evaluated 13 DPB patients [seven men and six women aged 23-68 (mean, 46.2) years] who had undergone PFT, HRCT, and transbronchial or open lung biopsy prior to long-term, low-dose EM therapy (250 mg twice daily for more than six months). The interval between initial and follow-up study ranged from 7 to 32 (mean, 16.6+/-8.0) months, and we compared the changes in HRCT findings and PFT parameters before and after treatment. RESULTS: At HRCT after EM therapy, the extent of centrilobular nodules (p=0.006), peripheral bronchiolar wall thickening (p=0.02), and areas of low attenuation (p=0.011) decreased significantly, while FVC and FEV1 showed significant increases: FVC, from 2.47+/-0.83 to 2.74+/-0.95 (p=0.028); and FEV1, from 1.66+/-0.75 to 1.95+/-0.87 (p=0.02). As the extent of peripheral bronchiolar wall thickening (r=-0.609, p=0.047) and areas of low attenuation (r=-0.687, p=0.041) decreased at serial HRCT, FVC and FEV1 increased significantly. CONCLUSION: Long-term follow-up HRCT findings showed that for DPB patients, lowdose EM provides effective treatment. In addition, HRCT appears to be valuable for the objective evaluation of responses to EM therapy.