Abstract: A review of plant components possessing toxic properties provides information on toxicants which occur naturally in foods of plant origin. The nutritional significance, physicochemistry, distribution, physiological effects, and health hazards of natural toxic plant substances are discussed. The subject matter is classified according to the following categories: protease inhibitors; hemagglutinins (lectins); glucosinolates; cyanogens; saponins; gossypol; lathyrogens; allergens; aglycones causing favism; naturally occuring carcinogens; and miscellaneous toxic factors. Toxic compounds induced by processing (heat, acid and alkali treatment, bleaching, irradiation, solvent extraction, fumigation, and contamination) also are considered. It is concluded that constant monitoring and elimination of toxicants is needed if plant food sources are to be utilized to their maximum nutritional potential. (nm).