“…The method is now widely utilized, but it requires a specially programmed freezer to control the cooling and warming rate accurately, and such an apparatus is quite expensive. On the other hand, vitrification (solidification of a solution without crystallization owing to elevated viscosity during the process of cooling) can be performed rapidly and simply without any such apparatus (Rail and Fahy, 1985;Scheffen et al, 1986;Kono and Tsunoda, 1988;Nakagata, 1989;Kasai et al, 1990;Nagashima et al, 1991;Schiewe et al, 1991;Ishimori et al, 1992). Recently, we developed a rapid and convenient mean of cryopreserving mouse preimplantation embryos (including pronucleate stage mouse eggs) by vitrification using sucrose or raffinose as a component of the vitrification solution (Tada et al, 1993a(Tada et al, ,b, 1994.…”