This paper reviews the safety and efficacy of sublingual immunotherapy (SLIT) in the treatment of allergic rhinitis. The literature from 1986 through 2007 shows approximately a 6000-fold range in doses found to be effective with SLIT. However, recent studies in large patient populations have demonstrated a clear dose response with an effective dose range that appears to be equivalent to one to two times the monthly subcutaneous immunotherapy dose administered daily or weekly (ie, 15 to 30 microg of major allergen). Further study is needed to establish the optimal dose and dosing schedule for each formulation. Local reactions (eg, oral itchiness) are common, and serious adverse reactions, although rare, have been reported. Cost-effective analysis cannot be made until the effective dose is established. SLIT appears to be a promising treatment for allergic rhinitis, but it is currently considered investigational in the United States until a formulation approved by the US Food and Drug Administration is available.