Candida antigen is known to be the major causative agent of adult bronchial asthma, especially intractable asthma. High responsiveness of lymphocytes in bronchoalveolar lavage fluid (BALF) to Candida antigen has been reported in patients with intractable asthma. Therefore, IL-2 production of peripheral blood (PB) lymphocytes and BALF lymphocytes in patients with various types of bronchial asthma was evaluated to clarify the role of cellular immunity against Candida antigen in the pathogenesis of intractable asthma. IL-2 production of PB lymphocytes in intractable asthma patients was higher than in non-intractable asthma patients and normal controls (p<0.01). Patients with intractable asthma receiving prednisolone at a dose of over 10mg/day showed lower IL-2 production by PB lymphocytes than patients receiving prednisolone at a dose of under 10mg/day. The direct suppressive effect of prednisolone was also evaluated in a vitro study, which revealed that the suppression of IL-2 production was dose dependent in the range of therapeutic concentrations. IL-2 production by BALF lymphocytes against Candida antigen was also studied, and it was shown that IL-2 production was higher in intractable asthma patients than in non-intractable asthma patients (p<0.01). IL-2 production correlated significantly (p<0.05) with lymphocyte blastogenic responses against Candida antigen in patients with intractable asthma.