Healthy and normal nonhuman primates are required for many biomedical research studies. Although guidelines and regulations exist for the maintenance of healthy nonhuman primates which include standards for nutrition, sanitation, and the micro- and macro-environments, the 1985 amendment to the Animal Welfare Act (PL 99-198) mandated additional requirements with the introduction of the term "psychological well-being."

Since the passage of the Act, many investigators have been attempting to define "psychological well-being" in an objective and measurable fashion. To date, no one definition has been described which can be applied equally to all individuals or species of nonhuman primates. As a state of well-being is similarly difficult to describe universally for all human beings, it is not surprising that such a definition is at present lacking in the primatological literature.

Many means of measuring "psychological well-being" are currently used. The most commonly utilized measures include behavioral and physiological parameters. Erwin and Deni (1979) have described in great detail the abnormal behaviors frequently seen in rhesus monkeys (Macaca mulatta) maintained in laboratories (see Appendix 1). Similar descriptions for other nonhuman primate species are also available. Physiological measures, such as cortisol and ACTH levels as well as immune status tests (e.g., IgG levels) are objective values that can be monitored at regular intervals. However, the validity of relying on measures of stress as the sole determination of psychological well-being has not been verified. Also, the ubiquitous usefulness and reliability of any measure for even one species of nonhuman primates is unlikely as individual variation in situational responsiveness is high in nonhuman primates.