The recent elucidation of the inflammatory responses underlying asthma and allergic rhinitis has stimulated the development of new anti-asthma treatments, including numerous antileukotriene agents. These agents, which represent a new direction in targeted therapy, either antagonize the leukotriene receptor (e.g. zafirlukast) or block the synthesis of leukotrienes (e.g. zileuton). They have been used in preclinical and clinical studies involving normal subjects and patients with asthma or allergic rhinitis. These studies have generally supported the putative role of leukotrienes in the mechanisms of asthma and allergic rhinitis. With respect to asthma, the leukotrienes also appear to function as potent mediators of bronchoconstriction. The above cited results indicate that antileukotriene agents offer incremental improvements in airway caliber and may also attenuate the inflammatory response. Because they are orally administered, they should have the additional benefit of increasing patient compliance relative to other currently available treatments. In their current form, however, they may not be expected to replace the mainstays of current therapy but to act rather, as adjuvant therapy. Patients with relatively mild asthma may be able to achieve efficacy with an antileukotriene agent plus as needed beta-adrenergic agonists; patients with more significant disease might use antileukotriene agents as a supplement to another anti-inflammatory agent, such as cromolyn, nedocromil, or corticosteroids. Studies of asthma patients have confirmed the ability of antileukotriene agents to attenuate asthma-associated bronchoconstriction. Antileukotriene agents appear to significantly attenuate aspirin-, allergen-, and exercise-induced asthma, as well as the signs and symptoms of nocturnal and chronic asthma; they may have efficacy in other inflammation-associated disorders such as allergic rhinitis as well.