This study was undertaken to evaluate whether the therapeutic effect of pranlukast, a selective cysteinyl leukotriene (LT) C4/D4/E4 receptor antagonist, can be observed in patients with the non-atopic or atopic type of asthma, or in asthmatics taking oral steroids. Twenty-two patients with moderate to severe bronchial asthma receiving an inhaled corticosteroid (beclomethasone dipropionate) were treated with pranlukast (225 mg b.i.d.) for 4 weeks, and their peak expiratory flow (PEF) and asthmatic symptoms were monitored during the treatment period. In the patients with the non-atopic type of asthma (n = 13), an increase in their PEF was observed both in the morning and evening following a 4-week administration ofpranlukast, but the degree was slightly inferior to that in patients (n = 9) with the atopic type of asthma. On the other hand, no significant increase was observed in the patients (n = 6) taking oral prednisolone (PSL, 5-15 mg/day). Changes in the symptom score at the end of the 4-week treatment period were closely associated with those in the PEF values; namely, a significant improvement in symptom score was observed for patients with the atopic and non-atopic type of asthma, but no improvement for the patients taking oral PSL. Pranlukast, a selective LT receptor antagonist, will be a valuable asset in the treatment of bronchial asthma, especially asthma requiring no oral steroids.