This experiment investigated a method of bovine embryo bisection during hatching stimulated by a zona pellucida perforation. The method of bisection was intended to significantly lower cell loss which occurs during standard bisection. Blastocysts, obtained either in vitro or in vivo, had their zona pellucida perforated by puncturing or slitting near the inner cell mass and subsequently were cultured in vitro. During culture, hatching was characterized by the extrusion of the inner cell mass as well as trophoectodermal cells through the opening in the zona pellucida. At a certain point the hatching the blastocyst took on a figure eight shape. Cutting the narrow bridge of cells which connected both parts of the embryo led to a splitting of the embryo into two equivalent parts. The experiment determined the factors responsible for effective hatching stimulated by earlier zona pellucida perforation. The optimal stage of bovine embryo development for obtaining the highest proportion of eight-in-shape hatching was late blastocyst. At this stage eight-in-shape hatching occurred in 50.4% of the embryos (137/272) while in the case of middle blastocyst 28.3% (17/60) and expanding blastocysts 15.3% (11/72). In the cases of puncturing and slitting the zona pellucida there was a similar proportion of eight-in-shape hatching, 137/272 (50.4%) and 93/190 (48.9%), respectively. Demi-embryos produced from thirty-five blastocysts bisected by the eight-in-shape method (modified bisection) were transferred into 41 recipients. Seventeen recipients became pregnant. All 17 calved, resulting in 20 calves, including 4 sets of monozygotic twins. In the control group there were 13 recipients which received halves obtained from conventional blastocyst bisection. Two recipients became pregnant, resulting in 3 calves, including 1 set of monozygotic twins. It can be concluded that the developed procedure of splitting embryos during stimulated hatching may be an alternative to standard embryo bisection.