A heart-lung transplant recipient with pulmonary disease caused by the rapidly growing nontuberculous Mycobacterium chelonae and obliterative bronchiolitis is presented. The clinical features, course, and management of the mycobacterial disease and the obliterative bronchiolitis are discussed. The role of transbronchial lung biopsy in determining the significance of rapidly growing mycobacteria in pulmonary specimens and in diagnosing infection and rejection is emphasized.