The NIH Animal Genetic Resource (NIHAGR) maintains several animal species, and many invaluable genotypes within a species, which are used as models in biomedical research. To protect this germ plasm, an embryo bank was established as an economical means to indefinitely preserve these stocks and strains of rodents and rabbits. Cryopreservation of embryos has other benefits for genotype management such as safeguarding against loss of germ plasm from disease, reproductive failure, natural catastrophe or genetic contamination. The cryobank minimizes changes due to genetic drift by providing a resource from which to periodically rederive defined genotypes for restandardization of foundation breeding colonies. As a recognized repository for laboratory animal species, the NIHAGR routinely provides breeding nuclei upon request throughout the biomedical research community. Rather than shipping live animals, cryopreserved embryos represent a simpler, more humane and easier method to transport requested germ plasm worldwide. Another important impact of embryo handling, cryopreservation, and transfer procedures is to eliminate the vertical transmission of some murine diseases. Genotype and species differences continue to impact on the efficiency of this is effort. - mouse embryos, cryopreservation, embryo banking, animal models