SUMMARY/ABSTRACT This proposal is a request to purchase and install pen housing for groups of nonhuman primates. These pens will be used primarily to house harem breeding groups of pigtail macaques (Macaca nemestrina). The Washington National Primate Research Center (WaNPRC) manages the largest domestic breeding colony of the pigtail macaque, M. nemestrina, to provide animal models for use in biomedical research. To save costs, the bulk of the breeding colony is housed at the WaNPRC’s Arizona Breeding Colony (ABC). However, this requires that animals be transported to Seattle for research assignments. Some research projects require the use of pregnant animals or pre-weaned juveniles, and it is necessary to breed animals in Seattle to meet these needs. Currently this breeding is performed in a timed-mating pair-housing situation. Installation of breeding pens in Seattle will increase production and efficiency while improving animal welfare. Housing animals in harem groups will eliminate the need for monitoring female reproductive cycles, scheduling mating days, and introducing breeding pairs. Housing the breeding animals in pens rather than individual cages improves overall animal welfare in two ways: Socialization in groups provides significantly improved psychological well-being when compared to single housing or even pair housing, and the increased total space (horizontal and vertical) in pens compared to cages improves both physical and psychological well-being. The cost of pens is significantly lower than the cost of cages per sq ft of floor space. In summary, this project will: 1) Increase efficiency of Seattle breeding program. 2) Improve animal welfare by increasing socialization and housing space. 3) Increase animal availability and decrease lead time for initiating research projects.