Abstract: The effectiveness of adriamycin (ADR) in the treatment of cancer has been limited by the development of drug resistance. Verapamil and ligustrazini were found to show significant potentiating effect on the cytotoxicity of ADR in vitro and decreased the IC₅₀ of ADR by 84.85% and 30. 82% of the resistant line, respectively, and no effect was found on the IC₅₀ in the sensitive line. The Glutathione-S-transfers activity of ADR--resistant and sensitive mouse EAC was determined in vivo. The activity in resistant cancer was 1.72--fold higher than that in sensitive cancer. Administration of verapamil or ligustrazini decreased the GST activity of resistant EAC by 35.50% or 26.05%, respectively and no effect was observed on sensitive cancer. The results show that verapamil and ligustrazini can reverse partly the ADR--resistance in resistant mouse EAC.