This study investigated changes in hormone levels and social behavior during late pregnancy and early lactation in rhesus macaque abusive and nonabusive mothers. All subjects lived in large social groups in outdoor corrals. Estradiol and progesterone levels increased to a peak the week before parturition, dropped after parturition, and remained low thereafter. The hormonal profiles of abusive and nonabusive mothers were generally similar. There were few changes in social interactions involving contact, grooming, or aggression across pregnancy or lactation, and minor differences between abusive and nonabusive mothers. The transition to motherhood was accompanied by a reduction in active grooming and an increase in aggression, and such changes were more marked for abusive than nonabusive mothers. Some individual differences in social behavior were correlated with hormone levels during pregnancy, but not lactation. These findings suggest that although the endocrine changes underlying the periparturitional period may affect female social behavior, some of the social changes associated with motherhood are likely to reflect the presence of infants.