Evidence from young primates indicates that even a brief period of separation from the mother or other attachment figure can have a number of physiological consequences for the infant. These effects include increases in sympathetic activity, changes in neurotransmitter levels, and increased activity of a neuroendocrine system associated with stress--the pituitary-adrenal system. In the past, it has been possible to study such questions only in primates because other commonly studied species (e.g., laboratory rodents) were not thought to show true infant-mother attachment. With the expense of primate research, the increasing demand for primate subjects, and the dwindling populations of wild primates, an alternative animal model would be beneficial. It appears that guinea pig mothers and infants may display a "true" attachment. Moreover, both infant and mother guinea pigs exhibit activation of the pituitary-adrenal system during brief (30 minutes) separation. The studies in the current research will further explore this question. Several issues will be addressed within this research, including the ontogeny of the separation response, the effect of environmental variables in determining responsiveness, and the specificity of the mother's response to infant separation. These studies will contribute to our understanding of the consequences of mother-infant separation and the processes of attachment and elucidate the nature of the stress response in young animals.