Hypersensitivity pneumonitis versus invasive pulmonary aspergillosis: two cases with unusual pathologic findings and review of the literature. Two brothers simultaneously exposed to moldy hay, who developed differing forms of Aspergillus-related lung disease, are presented. Patient 1 developed a true case of hypersensitivity lung disease, whereas his brother developed invasive aspergillosis with bronchoalveolar lavage eosinophilia and unusual pathologic features including tissue eosinophilia. The possible overlap between hypersensitivity pneumonitis and invasive aspergillosis in the immunocompetent host is discussed. 