Over 145 extracts of vegetables, fruits, herbs, spices and beverages which are consumed regularly in the European diet have been surveyed for potential anti-carcinogenic activity using an assay which measures the induction of NAD(P)H: (quinone acceptor) menadione oxidoreductase (quinone reductase, QR) activity in murine cells challenged with solutions of potential inducers. When appropriate the study has included extracts prepared from cooked and autolysed material. The results indicate that extracts of some brassicas, legumes (peas), lettuces, red pepper, grapefruit and some herbs including basil, tarragon and rosemary are inducers of QR activity. Inducing activity is strongly dependent on processing and on variety.