There was no difference between DMSO [dimethyl sulfoxide] and ethylene glycol in the survival of mouse embryos frozen to -79.degree. C, but significantly higher (P < 0.001) survival was obtained with ethylene glycol after freezing to -196.degree. C. Eight-cell mouse embryos were stored for 3 h, 30 or 180 days at -196.degree. C in the presence of 1.2 M-ethylene glycol. The survival of the embryos was 76, 71 and 78%, respectively. A further test of viability of the mouse embryos frozen to -196.degree. C in the presence of ethylene glycol was made by transfer of the embryos to the uterine horns of pseudopregnant recipients. To examine whether ethylene glycol must permeate 8-cell mouse embryos to protect them against freezing damage or not, the embryos were exposed to 1.2 M-ethylene glycol at 0.degree. C for various periods after the direct addition of phosphate buffered salt solution, solution containing ethylene glycol and frozen to -79.degree. C. Results demonstrated that permeation of ethylene glycol may not be required to protect 8-cell mouse embryos against freezing damage. For the 1st time it was shown that ethylene glycol is able to protect 8-cell mouse and rat embryos from freezing damage, and ethylene glycol might be applied successfully as the cryoprotective agent to embryos of other species.