Abstract B-cell acute lymphoblastic leukemia (B-ALL) is characterized by a neoplastic proliferation of precursor B cells that have blast cytomorphology and immature immunophenotype. Following treatment of B-ALL, flow cytometry is utilized to detect minimal residual disease (MRD), which aids in monitoring therapeutic response and informing prognosis. In our institution, the BD FACSCanto cytometer is used in conjunction with two standardized 8-antibody EuroFlow panels to detect MRD in B-ALL patients. The objective of this study was to validate a new 18-color B-ALL MRD panel for bone marrow aspirate specimens to be run on a BD LSRFortessa cytometer, with the intention of improving sensitivity and consolidating the testing into one antibody panel. The proposed panel consisted of 22 antibodies, some of which were stacked within the same fluorescence channel, in addition to a viability stain. Twelve bone marrow aspirate specimens collected in 2023 (five positive and seven negative B-ALL MRD specimens) were stained with the new antibody panel and analyzed on the Fortessa cytometer. CD45 dim, CD19-positive blasts were analyzed using BD FACSDiva Software. For the five specimens previously reported as B-ALL MRD-positive using the EuroFlow panels, we were able to detect phenotypically identical B-ALL cells with the 18-color panel. A paired t-test done on the five MRD-positive specimens showed no significant difference in the percentage of residual B-ALL cells (out of total viable cells) measured by the 18-color panel when compared to the EuroFlow panels (EuroFlow/18-color: 0.0096%/0.0097%, 0.024%/0.012%, 0.94%/0.99%, 0.85%/0.85%, 0.022%/0.017%; p=0.58). All seven specimens that were previously reported as B-ALL MRD-negative using the EuroFlow panels were also negative for residual B-ALL cells when stained with the 18-color panel and analyzed on the Fortessa cytometer. The antibody cost per test of the EuroFlow panels ($20-$25, ~$44 for both panels) and new 18-color panel ($63) were calculated based on the unit cost of each antibody aliquot and the required volume of reagent per test. In summary, the new 18-color B-ALL MRD panel run on the BD LSRFortessa cytometer appears to provide similar results as the EuroFlow panels run on the BD FACSCanto cytometer. Although compared to the two EuroFlow panels, the single 18-color panel is more expensive per test in terms of antibodies, it may be preferable when there is scant tissue (such as cerebrospinal fluid) as there may not be enough material to run both EuroFlow panels.