Trans-zearalenone, a resorcylic acid lactone, also known as F-2 toxin, is a nonsteroidal estrogenic mycotoxin produced by numerous species of Fusarium. As a result zearalenone is found in a number of cereal crops and their derived food products. A closely related substance "zeranol" (zearalanol) is at present being used in the United States and Canada as an anabolic agent in beef cattle. Zearalenone has been implicated in numerous incidences of mycotoxicosis in farm animals, especially pigs. In this report the health risks to Canadians due to the presence of zearalenone in food products have been evaluated. The first part of the report deals with the physicochemical aspects, mycology, laboratory production, and natural occurrence in plant products and animal products of zearalenone. The stability of zearalenone in foods and feeds, the effects of food processing, and the removal from foods and feeds by physicochemical means are also discussed. From these data the daily exposure of Canadians to zearalenone from food consumption has been estimated to be in the range of 0.05-0.10 microgram/kg b.w./day (mean and 90th percentile of eaters, respectfully) for young children, the highest consumption group on a body weight basis. The second part of the report deals with the metabolic disposition of zearalenone as well as the available toxicity data base of zearalenone in laboratory animals, farm animals, and humans. Studies in various species (rodents, rabbits, pigs, monkeys) including man have shown that zearalenone has estrogenic and anabolic activity. Its major effects are on reproduction, including reproductive organs and their function, leading to hyperestrogenism. Zearalenone has been implicated in numerous incidences of hyperestrogenism in farm animals, especially pigs. For reproductive effects a no adverse effect level (NOAEL) of 0.06 mg/kg b.w./day was estimated for the pubertal pig, the most sensitive species tested. Important differences in the biotransformation of zearalenone were noted, with greater amounts of alpha-zearalenol, the more estrogenic metabolite, formed in man and the pig compared to rodents. In addition, the biological half-life of these substances was longer in man than in other species tested. The binding of zearalenone to estrogen receptors was approximately 20-fold lower than that seen with 17 beta-estradiol in several assays.(ABSTRACT TRUNCATED AT 400 WORDS)