Effects of carotenoids in cellular and animal systems. It has been suggested that carotenoid pigments may function as chemopreventive agents for reducing the risk of cancer in humans. Part of this suggestion rests on epidemiological evidence, and part rests on work done in cellular and animal systems. In this article, the experimental evidence for carotenoid inhibition of mutagenicity, malignant transformation, tumor formation, and immunoenhancement is reviewed. Although a mechanism for these effects cannot yet be identified, it is clear that the overwhelming evidence in these systems would indicate that carotenoids exert an important influence in modulating the actions of carcinogens. 