Tea polyphenols, (-)-epigallocatechin galate in pariticular, were examined for their modulating effects on the drung resistance KB-A-1 cells and drug ensitive KB-3-1 cells. Both KB3-1 and KB-A-1 cells were queally sensitive to tea polyphoenol and (-)-epigallocatechin gallate. When 10μg/ml (-)-epigalllocatechin gallate or 40μg/ml tea polyphenol were persent simultaneously iwth doxorubicin, the IC50 of doxorubicin on KB-A-1 cells decreased form 10.3±0.9μg/ml to 4.2±0.2 or 2.0±0.1μg/ml. Tea polyphenol and (-)-epigalloctechin gallate enhancedthe cytotoxicity of doxorubicin on KB-A-1 cells by 5.2 and 2.5 times, respectively, but did not show a mdulating effct on KB-3-1 cells. Both tea polyphenol and (-)-epigallocatechin gallate showed reversal effects on the multidrug resistance phenotype.