DNA-breaking activity of heat-treated juices from 24 kinds of vegetables and fruits in the market was analyzed by use of agarose slab gel electrophoresis. 1. DNA-breaking activity was detected in the heat-treated juices from pumpkin, burdock, eggplant, shiitake, Chinese cabbage, celery, whelsh onion, Chinese leek, spinach, cucumber, garland chrysanthemum, green pepper, cabbage, onion, carrot, pear, kaki, tomato, garlic, radish and orange, while the activity was not detected in those from apple, pineapple and lemon. 2. Cu^<2+> ion decreased DNA-breaking activity of carrot, onion and pumpkin, but slightly enhanced the activity of cabbage. 3. The activity of garland chrysanthemum, green pepper, garlic, tomato and cabbage was inactivated by phenoloxidase. These findings suggest that some vegetables and fruits in the market contain DNA-breaking substances such as polyphenol compounds.