Plasma immunoreactive leukotriene C4 levels in patients with Kawasaki disease. The incidence of wheezing in Kawasaki disease (KD) has been investigated retrospectively. We measured plasma immunoreactive-leukotriene C4 (i-LTC4) levels of patients with KD. Wheezing was observed in 32 (12.5%) of the 256 patients with KD. Patients who had a prior history of bronchial asthma wheezed more frequently than other patients. During the acute stage of KD, plasma i-LTC4 levels both of wheezing and nonwheezing were significantly higher than those of healthy children. During the convalescent stage, plasma i-LTC4 levels of wheezing cases were higher than those of nonwheezing cases. We speculate that LTC4 contributes to the appearance of inflammatory symptoms during the acute stage of KD. During the convalescent stage when patients were taking aspirin, the presence of wheezing was associated with increased plasma levels of i-LTC4. More attention should be paid to the appearance of wheezing during the course of KD, especially in those cases in which the patient has a prior history of bronchial asthma. 