Allergic rhinitis is estimated to affect as many as 40 million people in the United States on a regular basis, and even more individuals who have occasional symptoms. The disease is associated with a considerable burden on the healthcare system, accounting for a total of $7.9 billion in direct and indirect costs in 1997, and with significant adverse effects on patients' quality of life, including disturbed sleep and impaired function at work and school. The pathophysiology of allergic rhinitis is complex, involving inflammatory mediators and immune cells that produce allergy symptoms via multiple mechanisms. The first principle of clinical management of patients with allergic rhinitis is avoidance of exposure to allergens, but this measure can be very difficult, and most patients require pharmacotherapy. Allergy vaccine therapy may be an appropriate and necessary option in selected patients with allergies refractory to other treatment modalities.