It has been known that many drug resistant factors including p-glycoprotein related to anticancer drug resistance. It is assumed that Glutathione s-transferase (GST) is one of the resistant factors. In this present study, we examined the relationship between GST (especially GST-pi) and drug resistance, and also possibility of overcoming of drug resistance for GST-pi related drug resistance. We studied whether GST-pi directly related to anticancer drug resistance by transfection of GST-pi antisense cDNA into human colonic cancer cell line (M 7609). By transfection, cytosolic GST-pi concentrations decreased and sensitivity for adriamycin increased. It was confirmed that GST-pi directly related to some anticancer drug resistance including adriamycin. Moreover, we also have found that ketoprofen, which is an inhibitor of GST-pi activity, increased Adriamycin sensitivity. That is, partial overcoming of drug resistance was obtained. In future, it will be expected that GST-pi inhibitors etc are tried for overcoming of drug resistance.