Thirty-five-day-old juvenile guinea pigs exhibited higher levels of plasma cortisol following 60 min of exposure to a novel environment when tested alone than when in the presence of the mother. This effect occurred regardless of whether the offspring had been housed continuously with mother and littermates from birth until testing or had been rehoused with just littermates 1 or 2 days prior to testing. Offspring vocalized more when alone then when in the presence of the mother only if they had been housed continuously with her until testing. In addition, juvenile males reunited with the mother after 1 or 2 days directed sexual behavior toward her. The sexual behavior was not accompanied by a significant change in plasma testosterone levels, though there was an overall suppression of levels following isolation in the novel test environment. The results show that guinea pig mothers maintain the capacity to prevent their offspring from exhibiting a plasma cortisol stress response even when the offspring are well beyond weaning and have been housed apart from her for up to 2 days. This suggests the existence of filial attachment in juveniles under these conditions. Further, juvenile males appear capable of simultaneously directing filial attachment and sexual behavior toward the same female.