There are literally thousands of known agents with potential chemopreventive and antioxidant activity; however, the expanding list of natural and synthetic compounds makes it difficult to test every agent in the widely accepted 2-year animal bioassay and human clinical trials. Therefore, short-term screening assays are needed to sort out the most efficacious compounds for long-term animal studies. In the present study, the identification of chemopreventive agents with efficacious antioxidant potential was explored with a Cu2+-mediated Fenton-type reaction, coupled with oxidative DNA lesion detection by 32P-postlabeling. Several agents inhibited the formation of 8-oxo-2'-deoxyguanosine (8-oxodG), a benchmark oxidative DNA lesion, but ellagic acid, a polyphenol found in berries, offered maximal (>80%) inhibition of 8-oxodG formation. However, a well-known tea polyphenol, epigallocatechin gallate, along with silymarin and D,L-sulforaphane, exhibited a pro-oxidant effect, with 50-70% increase in 8-oxodG induction. In general, our results agree with the reported antioxidant - pro-oxidant activities of the compounds, rendering this in vitro screening assay to be useful in determining the antioxidant potential of compounds rapidly and cost-effectively.