Lycopene (Fig. 1),β-carotene, and lutein are the three most abundant carotenoids in the human diet (1). Of more than 600 natural carotenoids, lycopene is the most efficient singlet oxygen quencher, and is therefore a potent antioxidant (2,3). Although twice as efficient as 13-carotene at quenching singlet oxygen (3,4), lycopene has no provitamin A activity, so its potential pharmacological effects cannot be associated with vitamin A. Lycopene is found in food primarily as the all-trans isomer, the form that is biosynthesized by plants and found in tomatoes, watermelon, and pink grapefruit (5). However, when exposed to heat and light during cooking or food processing, lycopene will produce a variable mixture of all-trans-lycopene and cis isomers.