This project is to establish a colony of monozygotic non-human primate twins for biomedical research models and to develop the technology and in-house expertise for initiating work in inter- species embryo transfer in endangered primates. During the course of this research a nonsurgical embryo recovery technique which has been developed by the investigative team will be perfected for recovery of uterine stage embryos from rhesus monkey (Macaca mulatta) females. Recovered embryos (morula to blastocyst stages) will be microsurgically bisected into monozygotic twin demi-embryos (DE). The DE will be used to compare two culture systems (CMRL medium alone or with cocultured endometrial fibroblasts) for maintaining in vitro viability over 24 hours. Following culture, the DE will be stained with fluorescein diacetate to assess viability. The DE will then be fixed and stained to count the cell number or frozen for subsequent assessment of viability following cryopreservation. Ultimate success in producing a substantial colony of monozygotic non-human primate twins will provide uniquely valuable animal models for biomedical research.