The Cryopreservation R&D program area offers services for banking unique strains of mice by preserving their frozen germplasm in liquid nitrogen (-196? C). Cryopreservation provides a cost-effective alternative to maintaining strains no longer in use by allowing their removal from the shelf storage. Additionally, the laboratory has a storage capacity of 44,000 vials and as a back-up against any imponderable disaster;a number of vials from each strain are kept at the National Cancer Institute-Frederick Central Repository. To further cancer research, the Cryobiology Laboratory utilizes state-of-the-art techniques that make it possible to offer different options for preserving a given mouse strain. Such techniques include freezing embryos at different developmental stages, freezing ovaries, and freezing sperm. With these options we are able to cryopreserve most inbred, spontaneous mutant, or genetically engineered strains, while maintaining the genetic background and genotype.