The number of CD4(+) T-Iymphocytes, CD4/CD8 ratio, and the number of IL2R(+) T-Iymphocytes (CD25) were examined in 14 patients with bronchial asthma, and the results were compared in three different asthma stages : symptom-free stage, wheeze stage, and attack stage. 1. The proportion of blood CD4(+) T-lymphocytes was more decreased in patients with asthma attacks than in those without symptoms. The CD4/CD8 ratio was also more　decreased in patients with attacks than in those without symptoms. However, these differences were not significant. 2. The proportion of blood activated T cells (IL2R(+) cells, CD25) was significantly increased in patients with attacks than in those without symptoms. The proportion of activated T cells in 5 asthma patients was 2.9±0.8% in　symptom-free stage and 6.6±1.1% in attack stage(p<0.001). These findings show that numbers of activated T-lymphocytes in peripheral blood were increased during asthma attacks, and this increase suggests the participation of　activated T cells in the pathogenesis of asthma.