Minimal residue disease (MRD) is a state in which the tumor cells remain in the patient in the amounts unrecognizable with the standard cytological techniques. Flow cytometry is one of the basic methods for evaluation of MRD in precursor B-lineage acute lymphoblastic leukemia (PBLALL). The so-called simplified three-color analysis using the combination of CD19/CD10/CD34 antibodies has been proposed to detect MRD in the midcourse of induction therapy. Four-to-nine-color is presently used to identify MRD. One hundred and thirty-four bone marrow samples taken at different stages of therapy in 55 children with PBLALL were examined to estimate the possibility of using the flow cytometry technique using the 3-color simplified approach to determining MRD. The results of the simplified and standard approaches were compared in the samples stained with 6-8 monoclonal antibodies in the combinations that always included CD19, Cd10 and CD34. The comparison revealed that MRD had been incorrectly identified by the simplified method in 8.0, 17.6, and 75.8% of the patients on therapy days 15, 36, and 85, respectively. In addition, the content of residual tumor cells with respect to the threshold values more frequently proposed to stratify patients was found to be incorrectly calculated in some true positive samples. Thus, when the simplified approach was applied using the results of MRD detection to stratify the patients into risk groups, 16.0, 27.4, and 81.8% of the samples would yield incorrect information on therapy days 15, 36, and 85, respectively. Thus, the simplified approach to identifying MRD is most applicable on day 15 of therapy; however, there may be mistakes in this point of observation. This method used on day 36 more frequently yields incorrect results and is inapplicable on day 85.