Changes in leukocytes and eosinophils in 60 patients with non-infectious attack (NIA patients) were compared with those in 50 patients with infection-related attack (IRA patients). In 30 (50%) of the 60 NIA patients, eosinophilia without leukocytosis was observed on admission, and in 23 (76%) of these 30 patients eosinophilia disappeared within 2 weeks of admission. In 36 (72%) of the 50 IRA patients, leukocytosis without eosinophilia was observed on admission, and the periods from the onset of infection to admission were inversely correlated with leukocyte counts. In 22 eosinophilia patients among the 50 IRA patients, the periods from the onset of infection to admission were correlated with eosinophil counts for up to 40 days, and in 13 (76%) of 17 eosinophilia patients not receiving a long-term steroid therapy during admission, eosinophilia continued for more than 2 weeks even after anti-asthmatic and anti-infectious therapies. There was no significant difference in serum IgE levels between the two groups on admission. These results suggest that evaluations of leukocytes/eosinophils on admission and clinical courses are very useful in the management of asthmatic patients with or without bacterial infections.