To assess the influence of bilateral pulmonary hypertension on the success of lung allotransplantation, 19 dogs underwent bilateral simultaneous pulmonary artery (PA) banding. This elevated mean PA pressures from 17/6 to 41/15 mm Hg. Later left lung allotransplantation lowered mean PA pressure to 22/9 mm Hg, and blood flow measurements two weeks later showed 70% of PA flow to be through the graft. Mean survival of 36.4 days compared favorably with that of normal recipients. Slight pulmonary edema occurred in most grafted lungs and was severe enough to cause two deaths. Since in the clinical setting presence of diseased lungs may compel the graft to accept 50% or more of the blood flow, the shortest possible ischemic and nonventilation times must be arranged. Cardiopulmonary bypass was unnecessary in the presence of pulmonary hypertension 2½ times normal.