We investigated the long-term (3-30 months) therapeutic effects of low-dose (300-600 mg/day) erythromycin in 26 patients with diffuse panbronchiolitis (DPB). Significant improvements of pulmonary functions especially in %VC and PaO2 as well as respiratory symptoms were shown. However, erythromycin treatment was not associated with a significant change in surface phenotypes on peripheral blood lymphocytes (CD4, CD8, CD4/CD8). It is well known that serum levels of tumor-associated carbohydrate antigens such as SLX (sialylated Lewis X-i) and CA19-9 (sialylated Lewis(a)) are significantly elevated in patients with DPB. In the present study, 68.4% (13/19) of DPB patients showed marked elevation of SLX and 52.9% (9/17) showed marked elevation of CA19-9 levels in serum. These positive ratios were significantly decreased by erythromycin treatment to 31.6% (6/19) in SLX and 23.4% (4/17) in CA19-9. The mean values of each marker were also significantly decreased after erythromycin administration from 54.9 +/- 26.9 U/ml to 39.5 +/- 22.1 U/ml for SLX and from 70.5 +/- 77.4 U/ml to 28.8 +/- 37.4 U/ml for CA19-9.