Anti-immunoglobulin E (anti-IgE) (omalizumab), a humanized monoclonal anti-IgE antibody that binds to circulating IgE, has been studied in several large double-blind, randomized, placebo-controlled clinical trials to determine its pharmacokinetic characteristics, efficacy, and safety in ragweed- or birch pollen-induced seasonal allergic rhinitis (SAR). The consequences of readministering omalizulab after a lapse of time have also been studied. These studies have confirmed that serum-free IgE declines in a dose-related manner with such treatment and that omalizumab-induced declines in IgE correlate with symptom improvement. Whether omalizumab is administered intravenously or subcutaneously, its pharmacokinetics do not differ. A Phase II dose-ranging study demonstrated that the optimum efficacious dose of omalizumab for the treatment of seasonal allergic rhinitis is 300 mg administered subcutaneously. The dosing frequency, in terms of whether the antibody is administered every 3 or 4 wk, is based on the patient's baseline IgE level. With adequate dosing, nasal and ocular symptoms are significantly reduced, and quality of life is significantly improved. Omalizumab is safe and well tolerated and can be safely readministered in subsequent pollen seasons.