Abstract: Multidrug resistance (MDR) is the phe-nomenon observedin tumor cells that describes the simul-taneous emergence of cellular resistance to the cytotoxic attack by structurally and mechanism unrelated chemotherapeutic drugs.The mdr^-1 gene was sufficient to confer the MDR phenotype, including the expression of the P-Glycoprotein (P-Gp).P-Gp appears to play an im-portantrole in tumor cells by acting as an energy-depen-dent efflux pump toremove various drugs from the cell be-fore they have a chance to exert their cytotoxic effects.It is generally accepted that reversal or inhibition of P-Gp function in tumor cells is an important way for modulating MDR.It has been demonstratedin the laboratory that MDR mediated by the P-Gp may be modulated by a wide variety of compounds.These compounds, which include verapamil and cyclosporin, generally have little or no ef-fect by themselves on the tumor cells, but when usedin conjunction with antineoplastic agents, they decrease, andin someinstances eliminate, MDR.This paper will introduce somenew reversal agents and discuss their physical and chemical characteration and others.

Key words: multidrug resistance, P-Glycoprotein, reversal agents