Studies on early development have demonstrated the profound effects of early social experience on thebehavioral development and physiology of young rhesus macaques. Given these relationships, wehypothesized that rhesus macaques exposed to different nursery-rearing conditions may develop uniquebiobehavioral profiles. If this is true, the assessment of temperament may allow us to pinpoint sucxessfulrearing environments, thus improving the overall health of nonhuman primates that are raised in captiveenvironments. We conducted biobehavioral assessments in order to Qx}mine differences in thedevelopment of infants raised under four different peer-rearing conditions (continuous pairing (CP),intermittent pairing, CP with partner rotation, and intermittent rotational pairing) and compared theseanimals with data from a mother-reared control group. Overall, continuous rotationally paired animalswere most similar to mother-reared controls on most behavioral and temperament measures, suggestingthat more socially complex rearing environments (greater number of social partners) favor a more activebehavioral style. Cortisol profiles of mother-reared controls were similar to both CP groups, and thesethree groups had higher cortisol concentrations than the intermittent rotational-pairing group.In addition, intermittently paired infants displayed a significantly higher frequency of self-strokebehavior during a human intruder challenge, an abnormal behavior also known as floating limb which hasbeen shown to be a precursor of self-biting. Overall, the data are consistent with the idea that socialcomplexity in the nursery, as operationalized in our continuous rotational pairing, leads to a biobehavioralprofile that is most similar to that of infants raised妙their mothers in large, socially complex, cages.