In this study, we investigated the role of reductive activation of DOX by the human liver CPR in increasing its cytotoxic activity against human promyelocytic leukaemia cells exhibiting two different phenotypes of MDR related to the overexpression of P-glycoprotein (HL60/VINC) or MRP1 (HL60/DOX). This evidence concerns the gene ABCB1 and acute promyelocytic leukemia.