Epigallocatechin-3-O-gallate (EGCg) and related polyphenolic compounds found in tea are known to have antioxidative activities. However, they also have pro-oxidative activities such as generation of hydrogen peroxide. In this report, we investigated the effect on cells and showed the potential usage of EGCg in cell preservation. H(2)O(2) was generated from EGCg at concentrations of more than 300 microg/mL for 6 h at 37 degrees C, and high cytotoxicity for L929 cells were shown. In contrast, in the presence of 1 microg/mL catalase, the amount of generated H(2)O(2) was significantly low and cytotoxicity decreased markedly. This indicates that catalase eliminated H(2)O(2) generated by degradation of EGCg. Although H(2)O(2) generation was prevented, L929 cell proliferation was slightly inhibited in proportion to the concentrations of EGCg. L929 was exposed able to be 300 microg/mL to EGCg and 1 microg/mL catalase for maximum 18 days. EGCg inhibited the growth of L929 cells, and cell proliferation was restarted immediately after medium change for removing EGCg. We concluded that EGCg had a reversible growth inhibition when H(2)O(2) was eliminated from cell cultures.