Bronchiolitis obliterans organizing pneumonia (BOOP) is a pathologic entity characterized by intraluminal fibrosis of distal air spaces. Corticosteroids have been widely used for the treatment of this condition, and most patients showed a dramatic response to it. However, long-term treatment with corticosteroids, which often increases the risk of several undesirable side-effects, is usually required because a relapse tends to occur soon after termination of treatment. We administered erythromycin (EM) at low-dose (600 mg daily) for 3-4 months to 6 patients with BOOP, and obtained a good clinical, radiological, and physiological improvement. This suggests that EM can be successfully used, instead of corticosteroids, in the treatment of BOOP.