Cryopreservation of porcine embryos by traditional slow-rate freezing results in limited survival as a consequence of the high amount of cytoplasmic lipid droplets, which suffer irreversible damage at temperatures between +10 and–5 °C (Nagashima et al 1994, Pollard & Leibo 1994). Two methods may circumvent this problem: Firstly, removal of the lipid droplets by centrifugation and micromanipulation (Nagashima etal 1994, 1995). This improves survival rates, but the method is rather complicated and not applicable for routine use. Secondly, certain vitrification methods have been successfully applied to cryopreserve porcine blastocysts and, with a limited efficiency, morula stage embryos (Yoshino et al 1993, Kobayashi etal 1994, Kuwayama et al 1997).