Cryopreservation, or the freezing of embryos or sperm, has become a routine part of many research projects involving laboratory mice. In this article, we combine historical and sociological methods to produce a cryopolitical analysis of this less explored aspect of animal research. We provide a longitudinal account of mouse embryo and semen storage and uses in the UK and show that cryopreservation enabled researchers to overcome particular challenges-fears of strain loss, societal disapproval, and genetic drift-in ways which enabled the continued existence of strains and contributed to the scaling up of mouse research since World War II. We use the theoretical lens of cryopolitics to explore three different, yet overlapping, cryopolitical strategies that we identify. All share the ability to ensure the continued maintenance of genetically defined strains without the need for continually breeding colonies of mice. We argue that, in contrast to more common imaginaries of species conservation, the cryopolitical rationale can best be understood as purposefully not letting the strain die without requiring animals to live. The ability to freeze mice, then, had the potential to unsettle who the objects of care are in mouse research, from individual animals to the concept of the strain itself.