Results of 550 transfers of cryopreserved and thawed embryos were analyzed. A total number of 47 pregnancies was achieved (8.5% per embryo transfer). Significantly better results were obtained when no selection of embryos before cryopreservation was made (i.e. pronucleate stage embryos and patients with all embryos frozen) compared to the "spare embryos" group-14 pregnancies per 99 transfers (14%) vs. 33 pregnancies per 451 transfers (7%) respectively. Cultivation of thawed embryos before embryo transfer has a beneficial effect on implantation-19 pregnancies per 121 transfers (16%) in the group of cultured embryos vs. 28 pregnancies per 429 transfers (7%) in the group without cultivation. Cryopreservation significantly contributes to the effectivity of IVF and provides further possibilities for conception in addition to those achieved from the fresh cycle.