The heterogeneity of acute myeloid leukemia (AML) has been established by many new insights from molecular biological studies. In AML with favorable cytogenetic changes, KIT gene mutation has been known as a worse prognostic marker. Even in AML with normal cytogenetics, numerous molecular genetic alterations have been identified including internal tandem duplication of the FLT3 gene (FLT3-ITD), mutations in the NPM1 gene, mutations in the CEBPA gene, and partial tandem duplication of the MLL gene. Of these, FLT3-ITD has the most important prognostic implication. Insights into the molecular pathogenesis of AML have led to the development of more specific targeted agents. Currently, a number of agents have been explored in AML, including immunoconjugate of anti-CD33 antibody and cytotoxic agent (gemtuzumab ozogamicin: GO), tyrosine kinase inhibitors and farnesyl transferase inhibitor. These agents have shown promise in small studies. Large phase III studies will reveal whether these are effective in inducing complete remission and prolonging survival. Combining targeted agents with each other or with chemotherapy may improve the response rates. GO is the most promising drug, which has been evaluated in randomized trials by several major cooperative groups to determine whether the addition of GO improves the complete remission rate and overall survival. In the near future AML may be classified and treated by their molecular biological alterations.