Kawasaki disease, mucocutaneous lymph node syndrome, thought to be rare in the continental United States, occurred in epidemic form in New York City and adjacent New York and New Jersey in November-December, 1977. Aspirin and corticosteroids, reported to be ineffective treatment, were found to completely control the illness in affected children, provided adequate doses to achieve therapeutic blood levels were administered. Patients were found to malabsorb aspirin (and perhaps also to destroy it) and so required extraordinarily high doses during the acute phase; during recovery, doses had to be lowered to the usual range to avoid toxicity. The need for hospitalization and morbidity were reduced and, hopefully, mortality will also be reduced. The importance of not judging a drug ineffective in a disease without demonstrating adequate serum levels was again shown.