Gentuzumab Ozogamicin (GO) is a conjugate of an anti-CD33 humanized monoclonal antibody and the anthracycline calicheamicin with an attractive mechanism of action, since the CD33 antigen/antibody complex is rapidly internalized in the leukemic cell prior to drug delivery.4 Pivotal studies of (GO) as single agent at 9 mg/m2 in relapsed AML have shown an overall response rate of 28% and encouraging results have been obtained in phase II trials in which it has been employed in combination with other cytotoxic agents.5–8. The gene discussed is CD33; the disease is acute myeloid leukemia.