- Bronchiolitis obliterans (BO) is a serious complication of hematopoietic SCT (HSCT). The condition is believed to be the result of an inflammatory part of the GVHD. Although many BO patients receive immunosuppressive therapy, there is no clear evidence that therapeutic interventions have a positive impact. In the last 20 years, it has been recognized that macrolides have immunomodulatory effects beyond their antibiotic effect. Recent data suggest also that the use of macrolides in BO post HSCT may halt disease progression. Our objectives are to give the readers information on the background of BO post HSCT, to review the immunomodulatory properties of macrolides in general and specifically in pulmonary diseases, and to summarize the current knowledge of macrolide benefits in BO therapy. Research into macrolide immunomodulation for chronic pulmonary disorders, such as diffuse panbronchiolitis and cystic fibrosis, shows consistent positive effects. The use of macrolides for other types of pulmonary inflammatory complications is yet to be proved. The benefit for BO post HSCT was shown only in a small non-randomized trial. Additional in vivo research is needed before developing any firm conclusions.