Adverse experiences that occur during early critical periods of development modify activity of neuroendocrine systems, such as the hypothalamic-pituitary-adrenal (HPA) axis and oxytocin system. This dissertation examines the effects of nursery rearing, an established model of adverse early experiences, on activity of the HPA axis and oxytocin system in infant and adult rhesus macaques (Macaca mulatta). In addition, influence of oxytocin system activity on the HPA axis and behavioral reactivity was examined. In infant monkeys, nursery-rearing was associated with lower HPA axis, yet higher oxytocin system activity, following the acute stress of developmental assessment. Nursery rearing may result in dysregulation of the HPA axis and a lower overall set point of activity. Mother-reared infants demonstrated higher reactivity during the assessment, which likely reflects a protest response to maternal separation and the strong attachment bond formed in mother-reared infants. Higher oxytocin system activity, lower HPA axis activity, and lower behavioral reactivity during separation and testing in nursery reared monkeys support interactions between HPA axis and oxytocin system activity and corresponds with the pattern of rodent neuroendocrine activity in response to an acute stressor. At 8 months of age, infants were weaned and relocated to mixed-rearing social housing. Infants responded with increased HPA axis and oxytocin system activity that did not vary by rearing condition. Although there was no effect of rearing on overall oxytocin system activity, nursery-reared infants that had been reared with a surrogate-mother, versus rearing with peers, had lower hair cortisol concentrations than mother-reared counterparts at the time of weaning, further supporting the view that nursery-rearing confers a lower set point of HPA axis activity. In contrast, neither HPA axis activity, oxytocin system concentration, nor behavioral reactivity as measured by the Human Intruder Test varied as a function of rearing history in adult rhesus monkeys. This dissertation demonstrates that, although nursery rearing is associated with changes in HPA axis and oxytocin system activity in infant rhesus monkeys, early rearing experiences may not exert prolonged effects. Finally, these data provide some support for an interaction between the HPA axis and oxytocin system, although only during early development.