The goal of this proposal is to continue to support US Public Health Service (PHS)-sponsored HIV/AIDS research programs to serve the needs of internal and external investigators by expanding nonhuman primate (NHP) indoor-outdoor breeding space for high-priority NHP HIV/AIDS research studies utilizing simian immunodeficiency virus (SIV) and chimeric simian-human immunodeficiency virus (SHIV). The proposed new Primate Enclosures in a Natural Setting (PENS) crib-style animal shelter will comprise a total of 5,574 gross square feet (GSF) including (12) interior and (12) connected exterior animal runs as well as an interior central service breezeway to expand the capacity of animal holding and breeding areas on campus. Each of the (12) PENS units will adjoin a covered central breezeway for animal care and service access. The breezeway will have alcoves between pairs of units that will provide safe access and workspace clearances to the critical infrastructure for the building. Each interior pen will have a single personnel door for staff access as well as a vertical sliding animal door for movement of nonhuman primates during cleaning. The new PENS units are intended to be functionally and aesthetically similar to the existing adjacent PENS Crib Shelter, a previous NIH grant-funded project completed in 2011. That project included a Central Services building that will provide utilities infrastructure (high temperature/pressure wash-down water, low-voltage systems and power) to the proposed new PENS expansion shelter. Exterior circulation, landscaping and civil design will accommodate ease of access for personnel and equipment as necessary and serviceability of mechanical, electrical and plumbing utilities between the shelter and the service building. This project builds upon the earlier design and implementation of PENS at the ONPRC and success in demonstrating the utility of this design for breeding of SPF4 rhesus macaques for HIV/AIDS research. The resulting building will increase harem-style breeding facilities designed for small breeding groups assure knowledge of paternity and MHC Class I alleles, and will allow socialization of animals in matriarchal groups from birth to assignment. Failure to expand the breeding capacity will limit the Center's ability to support the research programs of our current and recently recruited NHP/AIDS core investigators. Further, it will compromise the ONPRC's ability to accomplish its mission as a national scientific resource for animals, expertise, and specialized facilities and equipment to scientists conducting infectious disease research in NHPs.