Kawasaki disease (KD) is an acute febrile illness of early childhood, in which the activation of monocytes/macrophages plays a central role in the development of vasculitis during the acute stage of disease. In this study we investigated peripheral blood T cells of 10 patients with KD, focusing on the Th1 and Th2 imbalance, using intracellular cytokine staining and analysis of the cytokine-producing T cells by flow cytometry. We observed a decrease in the numbers of IFN-gamma-producing, but not IL-4-producing, CD3+ T cells, during the acute stage. Our results suggest that there is an imbalance of Th1 and Th2 subsets during the acute stage of KD.