According to the US Department of Agriculture, in 2023 (the most recent year for which figures are available), the number of nonhuman primates (hereafter, “primates”) used in research, testing, and teaching in the United States was 65,823. This figure does not include the 41,989 primates who were not used in research that year but were held in laboratories for future use or within breeding colonies. The three most commonly used primate species are long-tailed (aka “crab-eating” or “cynomolgus”) macaques, rhesus macaques, and marmosets, but as many as 30 other monkey and prosimian (e.g., lemur, loris, and tarsier) species are also used. Monkeys are commonly used in neuroscience and in studies on immunology and infectious disease, especially HIV/AIDs.
Apes, which include chimpanzees, orangutans, gorillas, bonobos, and gibbons, are effectively not used in invasive research studies in the United States because they are listed as endangered under the Endangered Species Act (ESA). The ESA restricts the import of endangered species and requires special permits to use these animals in research that could cause them harm. Orangutans, gorillas, and gibbons were listed as endangered in 1970; bonobos and wild chimpanzees were listed as endangered in 1990.
Until 2015, however, invasive research was allowed with captive chimpanzees because this species was split-listed under the ESA, with captive chimpanzees listed as threatened (and therefore afforded fewer protections under the ESA). Additionally, special rules were in place that further reduced barriers and restrictions on the use of captive chimpanzees who had been bred in the United States so that invasive research could be conducted with them more easily.
In 2015, the US Fish and Wildlife Service (USFWS) announced that it had removed this split-listing and categorized all chimpanzees—both wild and captive—as endangered under the ESA. Later that year, the National Institutes of Health (NIH) announced that it would no longer support biomedical research on chimpanzees. These two actions effectively ended all invasive research on chimpanzees in the United States. The 2000 Chimpanzee Health, Maintenance and Protection (CHIMP) Act, which created and funded a federal chimpanzee sanctuary system, also required that all “retired” chimpanzees be moved to a sanctuary to live out the rest of their lives. Thus, in the United States, invasive research is now only conducted on monkey and prosimian species, not on apes. (Noninvasive behavioral and cognitive research is still conducted with apes at zoos, sanctuaries, and some research facilities.)
Monkeys who are used for research and testing are either imported from suppliers in other countries or bred at domestic breeding facilities such as NIH-funded National Primate Research Centers (NPRCs) and National Resources,1 other academic research facilities, contract research organizations (CROs), and other commercial suppliers. According to a 2023 report by the National Academies of Sciences, Engineering, and Medicine (NASEM), of the 31,844 primates who were imported in fiscal year 2021 (FY21), 30,649 (96%) were long-tailed macaques. Of the 4,874 primates who were domestically bred in FY21 at NPRCs and National Resources, 4,014 (82%) were rhesus macaques. Imported long-tailed macaques are largely used by private, for-profit entities (i.e., the pharmaceutical industry, CROs, and biotechnology companies), whereas primates used for NIH-supported (i.e., academic) research are typically rhesus macaques sourced from domestic breeders. Overall, for-profit commercial organizations that sell or experiment on primates accounted for approximately 42% of all primates held or used for research purposes in FY21.
Since 2020, the use of primates in research has received considerable attention from scientists, industry stakeholders, advocacy groups, and the media. The COVID-19 pandemic generated a marked increase in demand, since primates are often used in infectious disease research and vaccine and drug safety testing. At the same time, China—the largest supplier of long-tailed macaques to the United States—halted wildlife exports, including exports of long-tailed macaques. Together, these events caused a primate shortage in the United States and abroad. This shortage is at the center of a web of several other recent primate-related events, including an indictment over alleged international monkey laundering and smuggling, a fight over the endangered status of long-tailed macaques, and a push to expand domestic breeding of nonhuman primates. To read more about the current primate research landscape, see AWI Quarterly, spring 2025.
Refinements to Primate Care
Historically, many of the basic physical and psychological needs of primates were ignored by those conducting research with them. There was an unfounded concern that modifying the environment would introduce data-biasing variables and that the financial costs to accommodate the animals’ needs would be too great. As a result, primates were typically housed alone, in small, barren cages.
In 1985, the Improved Standards for Laboratory Animals (ISLA) amendments to the Animal Welfare Act (AWA) introduced substantial and important new requirements for animals covered by the AWA. Among them was the new requirement mandating “a physical environment adequate to promote the psychological well-being of primates.” The AWA regulations were thus updated to include requirements for social housing, environmental enrichment items, and exercise. The USDA—the federal department charged with enforcing the AWA—also published additional clarifications for meeting these requirement in its Final Report on Environmental Enhancement to Promote the Psychological Well-being of Nonhuman Primates.
AWI’s own Dr. Viktor Reinhardt (former laboratory animal advisor and current Scientific Committee member) was integral in raising awareness on the importance of social companionship for promoting positive psychological well-being for laboratory-housed primates. Dr. Reinhardt did more than spread awareness about the advantages of social housing: He also pioneered successful pair- and group-housing techniques so that primates could be housed socially without fighting and injuring one another. His research culminated in dozens of publications on the topic, beginning in the 1980s. Dr. Reinhardt also developed positive reinforcement training (PRT) practices that allowed primates to develop trust in their human caretakers and even voluntarily engage in research and medical practices such as blood draws, rather than being subjected to stressful forced restraint procedures.
The 1985 ISLA amendments and mounting evidence of the importance of social companionship notwithstanding, by 2003 only 46% of indoor-housed primates used in research were housed socially, and 5% of those “socially housed” primates were given access to a conspecific only through a mesh barrier or only intermittently (e.g., overnight or between studies) (Baker et al., 2007).
In 2011, another push for primate social housing came in the form of a revised edition of the Guide for the Care and Use of Laboratory Animals (Guide), which research facilities are required to follow if they are funded by the NIH or accredited by AAALAC International.2 This revised, 8th edition of the Guide (the edition currently in use today) calls for more enrichment and maintains that social housing should be the “default” condition provided to primates. The Guide acknowledges that inadequate social and environmental enrichment can lead to abnormal development and behavior and thus compromise animal welfare and scientific validity.
Nevertheless, researchers are still allowed to request social housing exceptions—for example, if they believe social companions will interfere with research goals or if they believe there is risk of harm from fighting. (Research by DiVincenti and Wyatt (2011) has suggested that risk of harm from pair housing is overestimated and the benefit of social housing is underestimated.) A 2014 survey by Baker (published in 2016, and the most recently available data of its kind) indicated that 65% of indoor-housed primates used in research were housed socially—a dramatic improvement from the 2003 levels, but a long way from the ultimate goal of social housing serving as the default scenario for all laboratory primates.
In addition to social companionship, the ability to exercise some level of control over their environment (i.e., agency) is also vitally important. Using positive reinforcement training to encourage animals to voluntarily engage in husbandry or research activities (rather than by using force) is an important way researchers can increase primates’ perception of agency and improve their welfare. In 2014, all surveyed research facilities reported using PRT to some degree, but only a quarter of these facilities reported using PRT with at least 50% of their research primates.
Climbing and perching are also important behavioral activities. The vertical dimension of the primate’s environment may be used for a variety of purposes, including rest and sleep, and to escape and feel safe from predators (in the laboratory, humans can be perceived as predators). Finally, primates require mental stimulation to avoid experiencing prolonged periods of boredom, which can have negative health consequences. Social housing, PRT, and provision of environmental enrichment are all methods that can enhance psychological well-being for captive primates.
Since its inception, AWI has been at the forefront of the push to improve conditions for primates in research. AWI worked toward the successful adoption of the AWA in 1966 and of the ISLA amendments in 1985, provided data encouraging significant changes in the 8th edition of the Guide, and has widely distributed extensive literature on the needs of primates in research that by law and ethical obligation must be accommodated to the greatest extent possible. AWI will continue to promote evidence-based improvements for the housing and handling of primates in research and encourage the reduction and replacement of animals as research subjects where appropriate. Presently, AWI scientists are conducting a mapping review to catalog the scientific literature regarding the impact of various social housing conditions on primate welfare.
1. The United States maintains seven federally funded NPRCs. Federal funding of primate research began in 1960, when Congress passed legislation that enabled the NIH—the nation’s largest public source of funding for biomedical research—to fund and provide resources to institutions to conduct research with primates. The aim of the NPRCs is to maintain breeding colonies, provide a source of centralized experience and resources, and carry out coordinated activities under the NPRC Consortium. Other primate centers in the United States also receive funding from the NIH but do not maintain NPRC status and receive funding from other federal or private sources as well. These include four institutions that serve as “National Resources” for domestic breeding colonies.
2. AAALAC International, initially known as the “American Association for Accreditation of Laboratory Animal Care,” changed its name to the “Association for Assessment and Accreditation of Laboratory Animal Care International” in 1996. In 2016, the official name was shortened to “AAALAC International.”