Cryopreservation of mouse embryos biopsied at 4-cell stage was investigated by ultrarapid freezing. Four-cell embryos were obtained from ICR mice on 55h after hCG injection. Zona pellucida of the embryos were partially dissected with a cutting pipet, and then single blastomeres were biopsied from the embryos followed by incubation in $Ca^2$+ and $Mg^2$+-free M16 medium for 30min. Biopsied embryos cultured for lh or 15h were frozen by ultrarapid freezing method using 3M DMSO or 5M glycerol as a cryoprotectant, respectively. The developmental rate of biopsied embryos after ultrarapid freezing and thawing to blastocysts was 81 % in the group of biopsied embryos cultured for lb and 98% in the group of biopsied embryos cultured for 15h, respectively. When biopsied embryos after ultrarapid freezing and thawing were transferred to the uteri of pseudopregnant recipients, normal live young were born. These results suggest that this freezing method can efficiently cryopreserve biopsied mouse embryos.