Graft eosinophilia was observed in lung biopsies from nine patients who received lung allografts. Five cases were associated with moderate to severe acute cellular rejection and responded well to steroid therapy. In this group the eosinophilia occurred early after transplantation and was associated with an elevated white blood cell count and occasional peripheral blood (one of five cases) and bronchoalveolar lavage (one of five cases) eosinophilia. A second group of four patients had graft eosinophilia due to infectious agents. In these cases patients frequently had underlying bronchiolitis obliterans (two of four cases) and developed tissue eosinophilia late after transplantation. Bronchoalveolar lavage cell profiles often demonstrated dramatic eosinophilia. Histologically, the biopsy specimens displayed an acute eosinophilic pneumonia, which was attributed to Aspergillus sp (two cases), coxsackie A2 virus (one case), and Pseudomonas maltophilia (one case). Two patients in this group died from infection. While eosinophils are a frequent cellular component of acute rejection reactions, they also may be the dominant cellular component in graft infection.