depending on the number of metaphases analyzed. FISH technique with a higher sensitivity, 10(-2)-10(-4), attempts to make up for one of the principal limitations of G banding which is the absence of metaphases, thus employing different probes and allowing the study of interphase nucleus. Our patients were monitored with both methodologies during the course of the disease looking for MRD. FISH is the best methodology for quantifying the abnormal clone until we can apply quantitative PCR routinely. It will also be important for the follow up of rearrangements for which we do not yet have molecular determinations available. Our findings are coincident with those of other research groups in the need of evaluating higher series of patients with different pathologies in order to arrive at conclusions allowing us to predict relapse with any certainty.