Allergic rhinitis is an IgE-mediated condition that produces inflammation of the mucosa of the nose, paranasal sinuses and, frequently, of the ocular conjunctiva. Allergic rhinitis causes a significant disease burden in terms of quality of life, lost productivity and medical treatment costs. One of the newest treatments approved by the FDA is Patanase (olopatadine hydrochloride) Nasal Spray, 665 microg/spray (OLO). Olopatadine is an antihistamine with selective H(1)-receptor antagonist activity. This review details the basic and clinical research on the olopatadine molecule and OLO nasal spray from 1996 to the present day. The reader will gain a better understanding of the pharmacology of OLO nasal spray, the clinical trial data that have established the efficacy of OLO nasal spray and the overall role of OLO nasal spray in the management of allergic rhinitis. Olopatadine nasal spray is one of the newest treatments approved by the FDA for the management of allergic rhinitis. OLO has a rapid onset of action, efficacy comparable to intranasal steroid sprays and is approved for seasonal allergic rhinitis in patients aged > or = 6 years.