The ability of (-)-epicatechin (EC), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG) to inhibit the growth of HCT 116 colorectal and Hep G2 hepatocellular carcinoma cells was examined by MTT and clonogenic assays (CA). The respective catechins inhibited the growth of HCT 116 more strongly than Hep G2. In MTT assay, IC(50) values of EGC and EGCG against HCT 116 grew smaller on prolongation of the exposure times of the cells to the catechins. In CA, however, these two catechins had IC(50) values ranging between 7.6+/-0.4 and 11.2+/-0.5 microM against the same cells regardless of the exposure times. EC showed much weaker growth inhibitions relative to the two aforementioned catechins.