Azacitidine has been undergoing clinical trials for almost 20 years and is internationally considered to have a useful place in the treatment of acute nonlymphocytic leukemia. However, its role in the various combinations for induction, intensification, maintenance, or relapse regimens has not yet been clearly defined. This review outlines the last 10 years' clinical experience with the drug in acute nonlymphocytic leukemia, analyzes what critical information has yet to be obtained, and suggests what phase III trials may still be feasible to gather that information.