Oxidative stress in humans is associated with damage to DNA, proteins, and biological membranes. Oxidative stress, which often arises as a result of an imbalance in the human antioxidant status, has been implicated in aging and a number of human diseases such as cancer, atherosclerosis, and rheumatoid arthritis. This study was performed to test the hypothesis that the consumption of fruit juices may improve antioxidant status in human plasma. Ten healthy men 25-26 years old were recruited for the study. After overnight fasting, study subjects were fed 150 mL of fruit juice, and blood was collected at 0, 30, 60, 90, and 120 minutes after consumption. After a 1-day wash-out period, subjects were fed with the next sample of fruit juice until all nine juices (pear, apple, orange, grape, peach, plum, kiwi, melon, and watermelon) had been evaluated. All juices were prepared from pure fruits ground in a home-style mixer. Dietary food records and anthropometric measurements were used to evaluate the nutritional status of subjects. The antioxidant activities of fruit juices were estimated by measuring antioxidant status in the plasma using dichlorofluorescein (DCF) fluorescence. Except for pear juice, eight kinds of juices exhibited potent antioxidant effects in human plasma. Within 30 minutes after consumption, orange, melon, grape, peach, plum, apple, and kiwi juices already effectively suppressed reactive oxygen species generation. This radical scavenging effect of fruit juices was maintained for up to 90 minutes post-consumption, but the relative DCF fluorescence had rebounded to near the initial levels at 2 hours post-consumption in most samples tested. Interestingly, however, grape juice continuously exerted persistent antioxidant activity until 2 hours after supplementation. These results suggest that the consumption of fruits or fruit juices may reduce damage from oxidative stress, and that this effect may be a consequence of the antioxidant activity of fruits in scavenging the reactive oxygen species generated in human plasma. However, long-term studies with more subjects are needed to provide additional supportive evidence and better characterize the antioxidant properties of natural fruit juices.