Eight-cell mouse embryos were frozen by using erythritol as the cryoprotective agent. The samples were cooled slowly (1 degree C/min) to temperatures between -15 and -75 degrees C before direct transfer into liquid nitrogen (-196 degrees C). The most effective concentration of erythritol for freezing of embryos was 0.6 M, and the optimal exposure time of embryos to 0.6 M erythritol at 0 degrees C prior to freezing appeared to be 60 min under the conditions used. The embryos in erythritol survived slow thawing (approximately 20 degrees C/min), only when cooled slowly to temperatures between -30 and -60 degrees C before transfer into liquid nitrogen, and survived rapid thawing (approximately 500 degrees C/min), only after transfer from -25 to -40 degrees C. The highest survival rates of slowly thawed embryos were obtained after transfer to -196 degrees C from -35 (63%) and -40 degrees C (64%), and the highest survival rates of rapidly thawed embryos were obtained after transfer from -30 degrees C (54%). Mouse embryos that survived freezing and thawing with erythritol as the cryoprotective agent were capable of developing to full-term fetuses.