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Freezing of mouse embryos in the oviduct.

The survival of 2-cell and 4-8-cell mouse embryos after freezing and storage in liquid nitrogen, -196 degrees C, was examined. Both isolated embryos and embryo-containing oviducts were frozen to -40 degrees C at a cooling rate of 0.3 degrees C/min, and then transferred to -196 degrees C for one week. They were rapidly thawed in a 37 degrees C water bath at a rate of approximately 275 degrees C/min. Survival was assayed by in vitro cultivation of thawed embryos. The results indicated that freezing 8-cell mouse embryos directly or in the oviducts, is a reliable procedure for storing 8-cell embryos. By the procedure used, survival rates of 64% for the directly frozen embryos and 66% for the embryos frozen in the oviducts were obtained.