To clarify the mechanism of late asthmatic response (LAR) which is related to intractable asthmatic attacks, cellular and humoral components at the sites of LAR were examined by bronchoalveolar lavage fluid (BALF) obtained after bronchial inhalation of Candida allergen. BAL examination was performed 2 hours after the LAR attack. The differential cell count was obtained and the level of leukotrienes (LTs) in the BALF and peripheral blood determined by high performance liquid chromatography. The percentages of eosinophils and basophil・mast cells and neutrophils were statistically high in the BALF after LAR compared with the level in the non-attack state (p<0.05 p<0.01). The level of LTC(4) was significantly higher in the BALF after LAR (p<0.01), and LTB(4) also showed a similar tendency at LAR. However, LTD(4) could not be detected in the BALF after LAR or in the non-attack stage. On the other hands, the percentage of neutorphils and LTB4 level in circulating blood showed a peak before LAR, and then decreased markedly during LAR. Eosinophils also decreased significantly during LAR, but the plasma LTC(4) level increased significantly during LAR. These findings suggest that neutrophils, eosinophils and basophil・mast cells play an important role in the pathogensis of intractable asthma attack and LAR following release of leukotrienes.