Oxytocin (OT) and arginine vasopressin (AVP) are neuropeptides that play critical roles in social behaviorcognition stress physiology and physical health. Dysregulation of OT/AVP systems (alterations in peptideconcentrations or the methylation of their receptor genes) has been implicated in adverse health outcomesincluding autism schizophrenia mood anxiety and personality disorders. OT is released in adult humans anddogs during affiliative forms of human-animal interaction (HAI) and HAI attenuates AVP release in dogs. ThusHAI may provide a safe and effective approach for stimulating endogenous OT release and inhibitingendogenous AVP activity. However it is unknown 1) whether HAI similarly stimulates OT release in children 2)whether HAI affects AVP release in humans (adults or children) 3) whether characteristics of the dog-childrelationship affect these responses and 4) how methylation of the OT receptor gene (OXTR) affects childrensattachment to pets or their physiological responses to HAI. The objective of this proposal is to identify how OTand AVP systems contribute and respond to HAI in children and to elucidate the relationships between thesemechanisms and the psychosocial processes of HAI. We will recruit a sample of typically developing 8-10 year old children who will engage in structured HAIsessions with a familiar companion dog or unfamiliar dog compared to a nonsocial control condition. In Aim 1we will measure short-term changes in OT AVP and cortisol in children engaging in HAI compared to a controlcondition. We hypothesize that through activation of neural networks that promote attention to social stimuli andencoding of social reward OT facilitates and responds to forms of social engagement that provide a sense ofsafety social support and emotional connectedness during HAI. We also hypothesize that HAI attenuates AVPrelease in children and that increases in OT coupled with decreases in AVP act to reduce hypothalamic-pituitary-adrenal activity. In Aim 2 we will measure short-term changes in OT AVP and cortisol in dogs during interactionwith children and assess coordination between dogs and childrens physiological responses. We hypothesizethat HAI will generate increases in OT and decreases in AVP and cortisol in both children and dogs. Wehypothesize that physiological responses will be coordinated between partners and associated with the extentof affiliative social behavior between the child and dog. In Aim 3 we will investigate relationships between childOXTR methylation (a biomarker for OXTR expression in the brain) and childrens attachment to pets andbehavior during HAI. We hypothesize that OXTR methylation will be negatively associated with childrensattachment to pets as well as the extent of their social engagement with dogs during HAI sessions. Ultimatelythis work will elucidate relationships between HAI and OT/AVP pathways advancing our understanding of thebiological mechanisms through which HAI affects child health and development.