Lycopene is a non-provitamin A carotenoid present in human blood and tissues. The major dietary sources of lycopene for the human are tomatoes and tomato products. Protective effects of a lycopene-rich diet on some types of cancer were suggested on the basis of epidemiological studies. There are several biochemical mechanisms potentially underlying the protective effects of lycopene. These include antioxidant activity such as the quenching of singlet oxygen and the scavenging of peroxyl radicals, induction of cell-cell communication, and growth control. In vitro and in vivo studies support this assumption. Dietary lycopene is absorbed and distributed in the human organism, but its bioavailability depends on various factors such as food processing or coingestion of fat. Little is known about the metabolism of lycopene. Potentially biologically active oxidation products of lycopene have been identified in human plasma.