A 57-year-old woman was referred because of exertional dyspnea, fever, and cough in June 2006. She had been employed to culture roses in greenhouses since 1991 and had developed a cough during the summer from 2003. Chest CT scan revealed diffuse centrilobular micronodules. Transbronchial lung biopsy specimens demonstrated alveolitis with lymphocytes and non-necrotizing epithelioid cell granulomas. After admission, both the patient's symptoms and laboratory data improved without medication. However, upon her return to work in the greenhouse, cough and exertional dyspnea reappeared. Aspergillus niger was detected in the greenhouse. Her serum was assayed for precipitating antibodies against various antigens, and precipitating antibodies against Aspergillus fumigatus, Aspergillus flavus, Aspergillus glaucus, and Aspergillus niger were demonstrated. In a double immunodiffusion test, cross-reactivity between Aspergillus niger and other Aspergillus species was indicated. Consequently, she was diagnosed as having hypersensitivity pneumonitis resulting from the inhalation of Aspergillus niger.