The biobehavioral consequences of psychogenic stress were examined using neuroendocrine and ethological methods in a captive colony of common marmosets (Callithrix jacchus jacchus). Specifically, hypothalamic—pituitary—adrenal (HPA) axis reactivity was evaluated as a function of gender and social status in four consecutive social environments [(1) stable heterosexual pairs; (2) isolation; (3) unstable peer groups; and (4) stable peer groups], by measuring both basal plasma cortisol, adrenocorticotropic hormone (ACTH) and β-endorphin concentrations and responsiveness of these hormones to dexamethasone, ovine corticotropinreleasing hormone (oCRH), and ACTH 1–24. Socially stressful conditions, such as isolation and peer group formation, were associated with increased HPA axis function and behavioral arousal, and individual profiles were related to gender and social status. Hormonal levels prior to group formation predicted subsequent status in peer groups. Basal morning concentrations of plasma cortisol, as well as cortisol responsiveness to dexamethasone suppression, were sensitive indices of HPA axis arousal during periods of social stress. The context-dependent development of hormonal and behavioral profiles, reminiscent of depression and/or anorexia nervosa, suggests that the common marmoset may be a useful model of psychiatric hypercortisolism.