Zearalenone (ZEN) is a toxic non-steroidal mycoestrogen produced by fungi that widely contaminate agricultural products, eliciting estrogenic responses by mimicking sex steroid hormones. Zearalenone is biosynthesised through a polyketide pathway by a variety of Fusarium fungi including Fusarium graminearum (Gibberella zeae), Fusarium culmorum, Fusarium equiseti, Fusarium crookwellense, Fusarium cerealis and Fusarium semitectum. Zearalenone and its derivatives share similar molecular mechanisms and activity with estrogens. They interact with the estrogen receptors (ERa and ERb) leading to functional and morphological changes in the reproductive system in both animals and humans. Zearalenone exposure is associated with the estrogenic syndrome and infertility in animals and premature thelarche and precocious puberty in girls. In animal models, it was found that prepubertal exposure to a low dose of Zearalenone, decreased breast cancer risk. When prepubertal rats were treated with 20 lg (1 mg ⁄ kg body weight) of Zearalenone, a significant reduction of both the incidence and multiplicity of DMBA-induced mammary tumours was noted. Zearalenone has been used to treat postmenopausal symptoms in women.