OBJECTIVE: Although an inability to form normal social attachments characterizes many forms of psychopathology, there has been little study of the neural basis of social bond formation. The primary purpose of this article is to describe a novel approach to the neurobiology of attachment. METHOD: The author reviews animal research on two closely related neuropeptides, oxytocin and vasopressin, implicated in the central mediation of attachment behaviors. These neuropeptides appear to be important for the initiation of pair bonds and parental behaviors as well as the infant's response to social separation. RESULTS: Both cellular and molecular studies have begun to reveal the mechanisms by which oxytocin and vasopressin neural pathways are regulated, leading to a preliminary understanding of how these hormones act within the brain to influence complex social behaviors. CONCLUSIONS: Although their function in the human brain has yet to be demonstrated, the available evidence suggests that oxytocin and vasopressin may prove to be important in the pathophysiology of clinical disorders, such as autism, characterized by an inability to form normal social attachments.Abstract Teaser