Part of the programme for the conservation of genetic resources of livestock in the Czech Republic is the cryopreservation of genetic material, which serves as a source of gene reserves. Currently, genetic material in the form of semen, embryos and oocytes is stored in genebanks. Mammalian sperm and embryos can be effectively stored in cryopreserved form in liquid nitrogen. Cryopreservation of oocytes, especially immature oocytes (germinal vesicle stage, GV), is challenging compared to cryopreservation of embryos. The low viability of thawed oocytes is mainly due to the size of the cytoplasm. Prior to cryopreservation, cells undergo dehydration and water replacement with cryoprotectants in the freezing medium. The larger the cell, the more challenging the process of dehydration and rehydration during the cryopreservation process.