Cruciferous plant foods contain large quantities of secondary plant metabolites that have been shown to inhibit chemically induced carcinogenesis in animals. One mechanism by which these chemicals may inhibit carcinogenesis is through the induction of enzymes, such as cytochrome P-450-dependent monooxygenases, glutathione S-transferases (GST) or epoxide hydrolases (EH), which metabolize carcinogens to more polar and excretable forms. Cruciferous vegetables of the Brassica genus (e.g. Brussels sprouts, cauliflower, broccoli) contain micrograms/g levels of an indolylmethyl glucosinolate commonly known as glucobrassicin. Upon disruption of the plant material, as in food preparation or chewing, a thioglucosidase-mediated autolytic process ensues generating indole-3-carbinol (I3C), glucose, and thiocyanate ion. At acid pH comparable to that found in the stomach, I3C forms to wide variety of condensation products ranging from linear and cyclic dimers, trimers and tetramers to extended heterocyclic compounds such as indolocarbazoles. Experiments reviewed here indicate that these indole-condensation products are the compounds responsible for some of the alterations in carcinogen metabolism observed in animals fed either I3C or any of several Brassica plant foods.