Previous preclinical studies have demonstrated that 3,4-methylenedioxymethamphetamine (MDMA) dose-dependently increases pro-social behavior and affiliative vocalizations in male nonhuman primates. As diagnostic criteria for several psychiatric diseases includes deficits in social functioning, examining the conditions under which MDMA selectively increases pro-social behavior may provide important insights into MDMA's potential as a therapeutic. One such condition is whether a subject's drug history has any impact on MDMA's ability to modulate social behavior. Here, we examined the ability of MDMA and d-methamphetamine (MA) to modulate pro-social behavior and affiliative vocalizations in four pairs of drug-naïve female squirrel monkeys (n=8). Doses of MDMA (0.1-1.0 mg/kg), MA (0.03-0.3 mg/kg) or saline vehicle were administered 10-min prior to observation sessions in which pro-social behavior (huddling, touching, and sitting within proximity to each other) was scored by a blind observer. Vocalizations were recorded and spectrograph analyses were used to characterize vocalizations as either affiliative or aggressive. Results show that MDMA dose-dependently increased pro-social behavior, with 1.0 mg/kg eliciting the highest pro-social scores in comparison to saline, whereas the dopamine-preferring releaser MA elicited little pro-social behavior in comparison to saline. In contrast, both MDMA and MA dose-dependently decreased all measures of vocalizations in females, with the highest total number of vocalizations evident after 0.1 mg/kg MDMA and the lowest total number of vocalizations evident at 1.0 mg/kg MDMA. Aggressive vocalizations were not elicited by either MDMA or MA. These results corroborate previous findings that MDMA, but not d-MA, increases pro-social behavior in male subjects and extends them to females. However, MDMA's increase in pro-social behavior appears to be de-coupled from vocalizations in drug-naïve female subjects. These data are in contrast to other reports in male subjects with drug histories showing that MDMA dose-dependently increases affiliative behavior and vocalizations. Taken together, these results suggest that sex and drug-history may be important variables in considering MDMA's efficacy in increasing pro-social behavior. Future studies will include drug naïve male subjects to investigate sex as a biological variable as well as other drugs that vary in selectivity for dopamine or serotonin release.