In the present study, the protective effect of water extracts from Hsian-tsao (WEHT) on DNA damage in human lymphocytes induced by UV-C and/or H(2)O(2) was evaluated using single-cell electrophoresis (comet assay). No toxicity was found in WEHT towards human lymphocytes. WEHT did not cause DNA damage at lower concentrations of 0.05 and 0.1 mg/ml, while it did cause slight DNA damage at a concentration of 0.5-2.5 mg/ml when compared with the control group. When WEHT was mixed with H(2)O(2) for reaction, it exhibited a slight inhibitory effect on DNA damage induced by H(2)O(2). Moreover, when WEHT and lymphocytes were irradiated by UV-C and then incubated for 35 min, the DNA damage decreased with an increase of the concentration of WEHT. Thus, WEHT could reduce UV-C-induced DNA damage, and WEHT had a more protective effect on UV-C than on H(2)O(2)-induced DNA damage. The protective effect of WEHT on DNA damage might be due to the fact that it contains polyphenol compounds and/or other active components.