Pulmonary infection is a major source of morbidity and mortality in recipients of lung allografts. The alveolar macrophage plays an important role in pulmonary host defense, and to fulfill this role it must have the ability to orient and migrate in the direction of a stimulus. Thus migratory activity was measured in cells recovered from lung transplant recipients by bronchoalveolar lavage. The primary patient group consisted of recipients who had no evidence of infection or rejection at the time of bronchoalveolar lavage. These patients were further subdivided into an early postoperative group (less than 6 wk posttransplant) and a late postoperative group (greater than 6 wk posttransplant). Other categories included patients with chronic rejection and a small group of patients with Pneumocystis carinii pneumonia. Alveolar macrophages recovered by bronchoalveolar lavage were assayed for migratory response to N-formylmethlonylphenylalanine and endotoxin-activated human serum. Stimulated migration of cells from healthy recipients obtained in the late postoperative course was similar to that of normal control subjects, but stimulated migration of cells from healthy recipients in the early postoperative period and those undergoing chronic rejection was greater than expected. Spontaneous migration was similar in all groups except those with P. carinii pneumonia, in whom it was greatly increased. We conclude that alveolar macrophage migration is not impaired in lung allograft recipients without apparent signs of infection or rejection and is in fact increased during periods of possible macrophage activation (shortly after transplantation and during chronic rejection).