HPLC was used to analyze doxorubicin in multidrug-resistance (MDR) human carcinoma cells. This method is novel, simple, sensitive, linear, accurate and precise. The minimal detectable concentration is 0.2 mug ml(-1). The reversal effects of tea polyphenols on MDR are elucidated by this method. The results indicate that the tea polyphenol, (-)-epigallocatechin gallate, is a potential modulator of MDR.