Kawasaki disease (KD) is the most common pediatric vasculitis and the most frequent cause of acquired heart disease in children in the U.S. Its etiopathogenesis is unknown, although T cell, B cell and monocyte/macrophage populations have all been implicated in the disease. The precise role played by T cells is unclear. Analysis of T-cell activation markers in peripheral blood has demonstrated conflicting data. Study of tissue samples, which could clarify this issue, has been limited. Expansion of T cells bearing V beta 2 and V beta 8 has been reported during the acute phase of the disease, suggesting that exposure to a superantigen may represent one of the etiologies. Other studies, however, have not confirmed V beta expansions of T cells; in fact, indirect evidence that a conventional antigen may be involved has been reported in certain patients. Together, these various studies suggest that the clinical entity of KD may be induced by a variety of etiologic agents.