The effects of cryoprotectant, equilibration time and cell stage on the survival of intact and bisected mouse embryos were determined following slow freezing. The number of blastomeres during in vitro development was counted by nuclei staining with Hoechst 33342. The post-thaw survival rates of intact 8-cell embryos, morula and blastocysts after slow freezing were 62.8, 76.8 and 60.0% in 1.5 M glycerol, and were 64.4, 75.6 and 57.6% in 1.5 M DMSO, respectively. The survival rates of ZP-free or bisected morula after slow freezing were 60.5 and 48.6% in 1.5 M glycerol, respectively. The number of blastomeres following in vitro culture for 24 to 28 hours of fresh and frozen morula was significantly (p$lt;0.05) different as 53.6±1.3 and 40.0±1.0, respectively. The mean number of blastomeres following in vitro culture for 24 to 28 hours of bisected and bisected frozen morula was 25.0±1.0 and 21.8±0.8, respectively. When 531 fresh, 282 frozen, 130 bisected and 66 bisected frozen embryos were transferred to 46, 23, 15 and 12 recipient mice, 26.9, 21.7, 14.6 and 7.6% of them developed to normal offspring, respectively.