The core-binding factor (CBF) leukemias comprise acute myeloid leukemia (AML) with t(8;21) and inv(16)/t(16;16), characterized by the presence of the AML1-ETO and CBFbeta-MYH11 fusion genes, respectively. These leukemia-associated genes can now be sensitively and reliably quantified by real-time reverse transcription polymerase chain reaction (RT-PCR) techniques and thus can serve as molecular targets for monitoring residual leukemia. Studies to date suggest that quantitative monitoring of minimal residual disease (MRD) in CBF-positive AML is useful in distinguishing patients at high risk of relapse from those in durable remission. Preliminary results of MRD monitoring by real-time RT-PCR in this subset of AML patients are promising and provide the basis for further evaluation by quantitative analysis in large prospective clinical trials.