Leucotrienes are synthesized from arachidonic acid. They are potent proinflammatory mediators that contribute to bronchial hyperreactivity. Antileukotrienes constitute a new group of antiasthmatic drugs. Zafirlucast, a leukotriene receptor antagonist, is now registered in Ireland and Finland for the treatment of mild to moderate asthma. We have studied the literature on antileukotrienes and have focused on their ability to prevent or inhibit symptoms in asthma. When patients with mild to moderate asthma are pretreated with an antileukotriene, the bronchoconstriction following provocation with cold, dry air, exercise or allergen is significantly reduced. ASA-sensitive asthmatics with adenoids and a lost sense of smell achieved a significant increase in FEV1s and regained their sense of smell after administration of an antileukotriene. Ongoing studies will tell us whether antileukotrienes have a significant steroid-sparing effect as compared with placebo, after which recommendations can be made concerning the future use of these interesting medicaments.