BACKGROUND: Peanut oral immunotherapy (OIT) is a promising approach to peanut allergy but reactions are frequent and some patients cannot be desensitized. The anti-IgE medication omalizumab (Xolair) may allow more rapid peanut updosing and decrease reactions. OBJECTIVE: To evaluate if omalizumab facilitated rapid peanut desensitization in highly allergic patients. METHODS: Thirty-seven subjects were randomized to omalizumab (n=29) or placebo (n=8). After 12 weeks of treatment subjects underwent a rapid one-day desensitization of up to 250 mg of peanut protein, followed by weekly increases up to 2000 mg. Omalizumab was then discontinued and subjects continued on 2000 mg of peanut protein. They underwent an open challenge to 4000 mg peanut protein twelve weeks after stopping study drug. If tolerated, subjects continued on 4000 mg of peanut protein daily. RESULTS: The median peanut dose tolerated on the initial desensitization day was 250 mg for omalizumab versus 22.5 mg for placebo treated subject. Subsequently 23 of 29 (79%) subjects randomized to omalizumab tolerated 2000 mg peanut protein 6 weeks after stopping omalizumab versus 1 of 8 (12%) receiving placebo (p<0.01). Twenty-three subjects on omalizumab versus 1 on placebo passed the 4000 mg food challenge. Overall reaction rates were not significantly lower in omalizumab versus placebo treated subjects (OR=0.57 p=0.15), although omalizumab treated subjects were exposed to much higher doses of peanut. CONCLUSION: Omalizumab allows subjects with peanut allergy to be rapidly desensitized over as little as 8 weeks of peanut OIT. In the majority of subjects, this desensitization is sustained after omalizumab is discontinued. Additional studies will help clarify which patients would benefit most from this approach.