Plants are proven sources of useful anti-tumor and chemopreventative compounds. Hence, identification of phytochemicals useful in dietary prevention and intervention of cancer is of paramount importance. The initial step in the formation of cancer is damage to the genome of a somatic cell producing a mutation in an oncogene or a tumor-suppressor gene. Fresh juices and organic solvent extracts from the fruits of strawberry, blueberry, and raspberry were evaluated for their ability to inhibit the production of mutations by the direct-acting mutagen methyl methanesulfonate and the metabolically activated carcinogen benzo[a]pyrene. Juice from strawberry, blueberry, and raspberry fruit significantly inhibited mutagenesis caused by both carcinogens. Ethanol extracts from freeze-dried fruits of strawberry cultivars (Sweet Charlie and Carlsbad) and blueberry cultivars (Tifblue and Premier) were also tested. Of these, the hydrolyzable tannin-containing fraction from Sweet Charlie strawberries was most effective at inhibiting mutations.