The incidence of respiratory allergy in the US has increased gradually over the past several years, and current estimates suggest that allergic rhinitis and bronchial asthma affect approximately 20% and 5% of the population, respectively. Rhinitis and asthma frequently coexist, and large-scale population surveys indicate that up to 38% of subjects with rhinitis have asthma, and up to 78% of subjects with asthma have chronic nasal symptoms. Safety concerns with the increased use of inhaled corticosteroids, the heterogeneity of the disease, and poor compliance with asthma medication regimens, point to the need for the development of safe and convenient oral therapies for asthma. Oral leukotriene receptor antagonists (eg montelukast) are the latest class of inflammation-modulating asthma drugs and appear to cause fewer long-term side effects than systemic corticosteroids and reduce the need for shorter-acting bronchodilator reliever medicines. However variability in response between patients has been observed and clinical experience with these agents is still limited.