Acute myeloid leukemia (AML) is the most common adult leukemia and has historically been treated with intensive multiagent chemotherapy. In May 2000, the U.S. Food and Drug Administration approved a new agent, gemtuzumab ozogamicin (Mylotarg) to treat patients who are 60 years and older in first relapse with CD33+ AML and not considered candidates for chemotherapy. Gemtuzumab is an antibody-targeted agent that binds specifically to the CD33 antigen that is found on the surface of more than 80% of patients with AML. The agent is administered via i.v. over two hours, and premedication with acetaminophen and diphenhydramine is recommended. Side effects include fever, chills, neutropenia and thrombocytopenia, and asymptomatic hypotension. Clinical remissions have been observed with gemtuzumab, and additional trials with this new agent currently are being conducted.