From the results of this prospective study (the largest published so far), we conclude that TEL/AML1 RQ-RT-PCR can conveniently complement MRD analysis for theprotocol-required risk stratification in childhood ALL if thesecond Ig/TCR target is not available or not adequately sensitive/specific. There is virtually no risk of false-positive result.However, as an under estimation of MRD level by TEL/AML1RQ-RT-PCR remains conceivable in a small percentage of samples (B5%), TEL/AML1 should be used as a second-choice target only and always in a combination with Ig/TCR-based technique.