Multiagent chemotherapy has significantly improved survival for childhood ALL.However,the relapse rate with current therapies remains at 20% to 30%.Numerous studies have proved that the minimal residual disease(MRD)is associated with relapse rate.The major methods for the detection of MRD include polymerase chain reaction(PCR)and flow cytometry(FCM).The measurement of MRD in childhood acute lymphoblastic leukemia offers the promise of individualized,risk-stratified treatment and the prediction for post-transplant outcome.