Here we report on the effect of an active compound of Sophora flavescens called matrine (0.1 mmol/L) combined with all-trans retinoic acid (1 ?mol/L) in alleviating retinoic acid resistance in acute promyelocytic leukemia-derived NB4-LR1 cells by differentiation induction, as can be seen by an induced morphology change, increased CD11b expression, and nitro blue tetrazolium reduction activity, and a decreased expression of the promyelocytic leukemia-retinoic acid receptor ? fusion gene and protein product. 