Allergic rhinitis affects 10% to 20% of Americans. It frequently coexists with other conditions, such as allergic conjunctivitis, sinusitis, and asthma, and is associated with impaired occupational function and performance in school, decreased quality of life, and increased health care costs. An efficacious agent with minimal adverse effects and a lack of drug interactions is needed to help simplify treatment of allergic rhinitis, especially in patients with comorbidities. Controlled studies of intranasal cromolyn sodium therapy for patients with seasonal and perennial allergic rhinitis are reviewed, and appropriate candidates for treatment with this agent are discussed. Cromolyn inhibits the degranulation of sensitized mast cells, thereby blocking the release of inflammatory and allergic mediators. It reduces symptoms of allergic rhinitis, and, when used prophylactically, cromolyn can prevent symptoms from occurring. Controlled studies comparing cromolyn with placebo, intranasal corticosteroids, and antihistamines have shown the efficacy of cromolyn in relieving rhinitis symptoms. In addition, because cromolyn is poorly absorbed systemically, it is well tolerated and not associated with drug interactions. Intranasal cromolyn has an excellent safety record, is available as an over-the-counter medication, and has been proved to be efficacious in patients with allergic rhinitis.