Premature thelarche/mastopathy is one of the mysterious diseases in pediatric endocrinology. Handbooks mention it as a harmless disturbance but for parents and physicians it's a difficult problem. A few epidemics were reported in the last decades but ethiology of the disease remain unclear until now. Authors observed increasing number of premature thelarche/mastopathy patients in the South-East Region of Hungary since 1989.Parents reported unusually frequently high amount of healthy foods (cereals, corn flakes etc.) in the diet of the patients. Extremly high concentration of estrogenic fusarium toxins was found at the analysis of these foods of cereal origin. In competitive receptor-assay system on human myometrial tissue high affinity of Zearalenon and Zearalenol was experienced to estrogen receptors. Sera of patients were investigated in reverse-phase HPLC-system using diode-array fluorescent detector. 5 of 36 examined serum samples contained 18.9-103.5 mcg/l Zearalenon. This is the first time to demonstrate estrogenic fusarium toxins not only in food samples, but on human estrogen receptors and in the sera of premature thelarche patients. These results may help to understand the background of the disease.