Two cases of aspirin-intolerant asthma whose polymorphonuclear leukocytes demonstrated hypersensitivity to sulpyrin in vitro were reported. The patients were 14- and 15-year-old girls. Aspirin and sulpyrin intolerance were confirmed by aspirin oral provocation test and bronchial sulpyrin inhalation provocation test. In those intolerant patients, preincubation of polymorphonuclear leukocytes with sulpyrin enhanced the calcium ionophore A23187-induced leukotriene C4 production as compared with those of healthy adults and aspirin-tolerant asthma.