This review examines the consequences of social deprivation on brain chemistry and behavior on rats. Although social deprivation produces wide-ranging behavioral and neurochemical effects, it appears that these effects are determined by a number of factors, the most critical factor being the age or developmental stage during the period of deprivation. Roughly, the effects examined in this review may be separated into three major developmental stages and each is related to deprivation of specific types of social interaction: preweaning/neonatal, postweaning/adolescent, and adult. The effects of social deprivation during each of these stages appears to be neurochemically and behaviorally specific. However, much of the research to date has failed to examine deprivation during specific stages, often combining deprivation of different types. Nonetheless, these modifications of experience produce animals of differing phenotypes, which could be characterized as pathological in nature in many instances, and may model particular aspects of human psychopathologies or perhaps the propensity to develop those phenotypic features.