The mass of evidence suggests that OB is a manifestation of allograft rejection in the time period later than that usually associated with acute postoperative rejection. Respiratory infection may serve to amplify (and possibly trigger) this process. A maintenance immunosuppression regimen utilizing cyclosporine A, prednisone, and azathioprine appears to be much more effective than an earlier regimen utilizing only the first two drugs. Aggressive surveillance utilizing prospective measurement of pulmonary function and arterial blood gases and a willingness to look for histologic evidence of OB with the earliest symptomatology has lowered significantly the mortality and the morbidity of this disorder at Stanford and elsewhere. We believe that the current ability to treat and even reverse this serious complication brightens the prospect of heart-lung and lung transplantation for assuming a role in the medical practice of the future.