Zearalenone (ZEA) is a macrocyclic lactone, estrogenic, diet-depending and fusaric micotoxin, which is produced on many kinds of cereals and feeds in the favourable conditions of humidity and temperature. The structure of ZEA is similar to the structure of estrogens and it enables binding to the estrogenic receptors. The stimulation of protein synthesis in the cells of the reproductive system, which causes intensification of cell proliferation, is one of the effects of ZEA actions. Oedema and vulva reddening are the clinical, external signs of ZEA intoxication in pigs. The aim of this study was to designate the degree of reproductive cell proliferation after low doses of ZEA were applied per os in sexually immature gilts with simultaneous monitoring of zearalenone and alpha-zearalenol levels in peripheral blood. The following were observed in the gilts examined fluctuations of zearalenone and alpha-zearalenol levels in blood, which were connected with entero-hepatic circulation and also numerous histopathological changes in ovarian follicle structure. These changes were present in the reproductive system of sexually immature gilts with a big contribution of PCNA-positive cells. The studies show that zearalenone application in sexually immature gilts caused ovarian follicle atresia and apoptoso-like changes in granule cells. Intensified cell proliferation, which was expressed with the growth of PCNA index, was observed in uterus and oviduct.