It is known that tumor associated carbohydrate antigens are significantly increased in the serum of patients with diffuse panbronchiolitis (DPB). We investigated carbohydrate antigens (SLX, CA19-9) in bronchoalveolar lavage fluid (BALF) obtained from 24 patients with DPB. The concentrations of SLX and CA19-9 were significantly higher in BALF from patients with DPB than those from healthy subjects (7 cases) and patients with pulmonary sarcoidosis (16 cases). No significant correlation was observed between either SLX or CA19-9 concentrations in the serum and BALF, and no significant correlation was observed between the concentrations of these carbohydrate antigens in BALF and clinical findings. Immunohistochemical study of SLX and CA19-9 in open lung biopsy specimens obtained from patients with DPB showed expression of SLX and CA19-9 on the bronchiolar surface epithelial cells and mucinous exudates in air spances. These results indicate that carbohydrate antigens are presumably increased in the pulmonary lesions of patients with DPB, and this increase causes high levels of these antigens in the serum. Furthermore, we investigated the change of concentrations of SLX and CA19-9 in BALF obtained from patients with DPB after erythromycin (EM) treatment. The concentrations of these two antigens were decreased after EM treatment.