A case of mucocutaneous lymph node syndrome in a 7 month-old boy in whom the usual therapy (acetyl salicylic acid, dipyridamole) could not prevent impairment of the clinical evolution is reported. As the role of circulating immune complexes had been suggested, and similarly with periarteritis nodosa in adults, 4 exchange transfusions were attempted. Their spectacular result, with a follow-up of 6 months, even though no circulating immune complex was detected, is a further argument for the immunologic pathogenesis of this syndrome.