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This study was carried out to determine the effects of cryoprotectants, freezing and thawing rates on the survival of 8-cell mouse embryos. The female ICR mice were induced to superovulated by intraperitoneal injections of 5 i.u. PMSG and 5 i.u. HCG given 48h apart and then were paired with males of the same strain. They were killed and embryos were flushed from the oviducts and uteri on 3 days after injection of HCG. Embryos were flushed with modified Dulbecco’s phosphate buffered saline and equilibrated with 1.5M-dimethyl sulfoxide (DMSO) or 1.5M-glycerol by 3-step procedure. The freezing rates of the embryos were 1^{circ}C/min from room temperature to -5^{circ}C and the embryos were seeded at -5^{circ}C. After being held for 3 min at the seeding temperature, the rates were 0.3^{circ}C/min from -5^{circ}C to -35^{circ}C. From -35^{circ}C to -70^{circ}C, the rates were divided into 0.1^{circ}C/min, 1^{circ}C/min and 10^{circ}C/min, respectively. After being held for 5 min at -70^{circ}C, the embryos were plunged directly into liquid nitrogen. The embryos were thawed at 4^{circ}C/min and 12^{circ}C/min from -196^{circ}C to 37^{circ}C, and for 2 min in 37^{circ}C water bath, respectively. The average number of ovulation points and embryos recovered were 42.7 and 34 appearing 79.5% recovery rate. Eight cell embryos in the embryos recovered were 26.3. The survival rates of embryos according to the freezing rates in the presence of 1.5M-DMSO were 73.5~80.6% at 0.1^{circ}C/min, 75.0~79.5% at 1^{circ}C/min and 52.8~54.7% at 10^{circ}C/min, but in the presence of 1.5M-glycerol were 62.9~67.6% at 0.1^{circ}C/min, 61.4~68.3% at 1^{circ}C/min and 25.5~30.2% at 10^{circ}C/min. The survival rates of embryos were not affected by the thawing rates.
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