The ability of mammalian eggs to support freezing is shown to be related to a reversible reorganization of their cytoskeleton induced by organic compounds used as protectants. 1,2 propanediol which is very effective for the successful freezing of early embryonic stages induces the formation of a fairly homogeneous gel within the cytoplasm in which the cortical layer of highly entangled polymers is no longer apparent. In vitro, propanediol influences specifically interactions between actin and binding proteins and induces the formation of microporous and homogeneous gels able to retain a significant fraction of water within their pores. When eggs are first submitted to a partial dehydration at room temperature they become able to support rapid freezing and thawing in the presence of propanediol probably because the remaining cellular water becomes osmotically inactive. This indicates that the rheological changes of the cytoplasm that occur in the presence of propanediol make the cell able to support the physical and chemical modifications that affect their microenvironment at low temperature.