Immunocompromised hosts usually develop invasive mycotic disease. Among many pathogenic fungi. Aspergillus spp, is the most common pathogen of respiratory infection. Early diagnosis of invasive type pulmonary aspergillosis is still difficult, and the treatment is usually difficult. Many investigations have recently suggested that detection of Aspergillus antigen from sera of the patients is useful for early diagnosis to save their lives. We have experienced a case diagnosed by the detection of circulating Aspergillus antigen by Pastorex Aspergillus, who was a 64-year-old female with the blastic crisis chronic myelogenous leukemia. After anti-leukemic chemotherapy, she suffered from pneumoniae with pleural effusions and severe hypoxia, which did not respond to antibiotics. At this point, her serum sample showed positive Aspergillus antigen by Pastorex Aspergillus. She was treated by intensive antifungal chemotherapy, and thereafter improved quickly. Titers of Pastorex Aspergillus were well correlated with her clinical course. The sensitivity of the test requires further improvement, but the specificity of the test is considered to be high enough for clinical use.