BACKGROUND A recombinant humanized anti-IgE mAb, omalizumab, forms complexes with free IgE, blocking its interaction with mast cells and basophils; as a consequence, it might be effective in the treatment of asthma. OBJECTIVE The purpose of this study was to evaluate the efficacy and safety of omalizumab in the treatment of inhaled corticosteroid-dependent asthma. METHODS In this phase III, double-blinded, placebo-controlled trial, 525 subjects with severe allergic asthma requiring daily inhaled corticosteroids were randomized to receive placebo or omalizumab subcutaneously every 2 or 4 weeks, depending on baseline IgE level and body weight. Inhaled corticosteroid doses were kept stable over the initial 16 weeks of treatment and tapered during a further 12-week treatment period. RESULTS Omalizumab treatment resulted in significantly fewer asthma exacerbations per subject and in lower percentages of subjects experiencing an exacerbation than placebo treatment during the stable steroid phase (0.28 vs 0.54 [P =.006] and 14.6% vs 23.3% [P =.009], respectively) and during the steroid reduction phase (0.39 vs 0.66 [P =.003] and 21.3% vs 32.3% [P =.004], respectively). Beclomethasone dipropionate reduction was significantly greater with omalizumab treatment than with placebo (median 75% vs 50% [P <.001]), and beclomethasone dipropionate discontinuation was more likely with omalizumab (39.6% vs 19.1% [P <.001]). Improvements in asthma symptoms and pulmonary function occurred along with a reduction in rescue beta-agonist use. Omalizumab was well tolerated, with an adverse-events profile similar to that of placebo. CONCLUSIONS The addition of omalizumab to standard asthma therapy reduces asthma exacerbations and decreases inhaled corticosteroid and rescue medication use.