The generation. of leukotrienes 84 (LT84) and C4 (LTC4) by leucocytes stimulated with Ca ionophore A23187 was examined in 71 patients with asthma (42 with atopic and 29 with nonatopic asthma) and 23 healthy controls. Of these patients,22 had SDIA (steroid-dependent intractable asthma). 1. The generation of LT84 and LTC4 by leucocytes was significantly more enhanced in patients with atopic, non-SOIA asthma than in healthy subjects, but not in patients with nonatopic asthma. The generation of LT84 and LTC4 in atopic asthma was significantly more decreased in patients with SOIA than in those with non-SOIA. 2. The LTC4 generation was significantly larger in attack stage than in attack-free stage of patients with atopic and nonatopic asthma when they had not SOIA. However, no significant difference was found in LT84 generation between attack and nonattack stages in these patients. 3. In patients with SOIA, no significant differences were observed in the generation of LT84 and LTC4 between attack and nonattack stages. The results suggest that IgE-mediated allergy and asthma attacks enhance and glucocorticoids inhibit the generation of LT84 and LTC4 by leucocytes.