P-glycoprotein (P-gp), the product of the MDR-1 gene, is a member of the ATP binding cassette superfamily of transport proteins Many discrepancies have been found regarding the role of P-gp expression in acute leukemias. Flow cytometric analysis is probably the most valuable tool for the detection of MDR in acute leukemias. P-gp functional analysis correlates better with treatment outcome than P-gp surface expression analysis. Not all P-gp + ve surface expression cases were having an active functioning pump and vice versa. The use of the multiparameter flow cytometric assay will add to the accuracy and sensitivity of P-gp expression and function estimation.