The joint team from Tanox and Ciba-Geigy received "investigational new drug" (IND) application approval, which is required for the first testing of a new substance in human subjects, for an anti-IgE antibody for the first time, from the U.S. Food and Drug Administration (FDA) in 1991. This was an important milestone in the development history of the anti-IgE program; Tanox scientists had anticipated major difficulty to receive IND approval for an anti-IgE antibody from the FDA, even though they had experimental data to show that CGP51901 would act differently from an ordinary anti-IgE antibody. Subsequently, Tanox/Ciba Geigy carried out a dose-escalating, double-blinded, placebo-controlled single-dose phase I clinical trial on 33 pollen-sensitive subjects with elevated serum IgE levels in Southampton, England. After resolving a few unexpected clinical findings, mainly the accumulating IgE and anti-IgE immune complexes, from the phase I trial, Ciba-Geigy and Tanox ran a successful phase II trial in 153 patients with severe seasonal allergic rhinitis toward mountain cedar pollens in three medical centers in Texas in 1994–1995. The positive clinical trial results, which showed increasing efficacy of CGP51901 over three different dosages (15, 30, or 60 mg in six bi-weekly doses) in improving nasal and ocular symptom scores, impressed the researchers and clinical investigators working on a similar anti-IgE program in Genentech.