[The viability of rat amd mouse embryos in low-temperature preservation].

Embryos of the laboratory rats and mice at the two-cell stage were frozen in different media with 1.5 M DMSO at a rate of 0.5-0.7 degrees/min to -40 degrees and the transferred into liquid nitrogen. Temperature of the crystallization initiation was -6 degrees. After thawed embryos were transplanted to foster mothers, these latter gave birth to normal offspring. The best results (38% of the total number of transplanted embryos in mice and 55% in rats) were obtained when using modified Whitten's medium for cryopreservation. Survival of the rat embryos in the NT-6 medium fell to 36% due, supposedly, to changes in pH accompanying the decrease in temperature. These results allow us to recommend modified Whitten's medium and the developed conditions of freezing-thawing for cryopreservation of the rat and mouse embryos.