Kawasaki syndrome (KS) is an acute multisystem vasculitis of infancy and early childhood associated with the development of myocarditis and coronary artery abnormalities. Despite the widely held belief that KS is caused by an infectious agent, there remains considerable controversy over its etiology. Recent immunologic and microbiologic studies suggest a potential role for staphylococcal and streptococcal toxins (superantigens) in the pathogenesis of KS. Confirmation of these findings could result in more effective diagnostic and therapeutic approaches to this common cause of acquired heart disease in children.