Eight-cell embryos collected from superovulated inbred strains and F1 hybrid mice were frozen by the microdrop technique developed in our laboratory. The technique based on pre-equilibration in medium with 10% glycerol, before transfer into vitrification solution, expel of embryos in 5 microliters to 20 microliters of vitrification solution directly into liquid nitrogen and thawing of microdrops in medium with 0.5 M sucrose was used. The behavior and morphological appearance of embryos during pre-freezing and post-thawing periods was documented. The efficiency of cryopreservation in microdrops was high, as documented by 90% to 100% of intact embryos after the freezing and thawing cycle. Furthermore, no zona pellucida damage was observed. The developmental potential of embryos frozen in microdrops was comparable with development of unfrozen embryos of the same genetic origin. After freezing and storage 83% to 93% of embryos developed to blastocysts and 73% to 92% embryos underwent "implantation" after 48 h and 96 h of in vitro culture, respectively.

Institute of Molecular Genetics Czechoslovak Academy of Sciences Praha