Background. This study was designed to assess which cells in transplanted lungs express endothelin-1 (ET-1) and if expression of the peptide can be used to discriminate between rejection and infection in transplanted lungs. Methods. Transbronchial biopsies (n-104) from 29 burnan lung transplant recipients were stained immunohistochemically for ET-1. Cells expressing ET-1 (pneumocytes, endothelial cells, airway epithelial cells, lymphocytes, and macrophages) were quantified and correlated with clinical histopathology findings. Results. ET-1 was expressed in airway epithelial cells (93% of the biopsies), infiltrating macrophages (86%), and lymphocytes (19%) but not in endothelial cells or pneumocytes. ET-1 expression did not vary with rejection, obliterative bronchiolitis, or infection. ET-1 expression did not correlate with age, grade of rejection, pulmonary function, or time after transplantation. Conclusion. In transplanted human lungs, ET-1 is expressed in airway epithelial cells and infiltrating macrophages, and expression does not vary with pathological processes. Therefore, immnunostaining for ET-1 probably cannot be used to discriminate between rejection and infection in transplanted lungs.