A major problem for research groups breeding inbred, mutant, and transgenic mouse lines is that many are poor breeders, or do not breed at all. This problem is often difficult to alleviate. Sperm banking can be used for mice (1–;3), but in some instances it is also important to bank the female genome (4). Superovulation and embryo transfer procedures are of little value for lines that produce few eggs or embryos, lines that die soon after birth or whose animals that die unexpectedly. In these cases, ovarian tissue grafting may provide a solution (5,6). Ovarian tissue grafting (transfer) is not a widely used technique, but it has been used successfully to propagate subfertile, infertile, and sterile mouse lines and is used by commercial breeders such as the Jackson Laboratories. In cases in which the mice carry transgenes that interfere with reproduction or shorten the animal’s lifespan (7–;10) ovarian transfer may be the only way of propagating the female line. Ovarian grafting has several significant advantages over embryo transfer (11). One advantage is that it is less age dependent. Tissue collected from fetal, newborn, juvenile, or adult female mice can all produce functional grafts (12–;18). A second advantage is that viable tissue can be “rescued” from recently deceased animals. If each “donor” ovary is cut into small pieces and each is grafted into a recipient, several breeding animals can be generated from each donor. Successful ovarian grafts develop quickly and usually restore normal estrous cycles in the recipient (her own ovaries are removed) within 2-6 wk.