The human placenta maintains high intracellular glutamate concentrations with no net glutamate transfer to the fetus. This study explores specific glutamate efflux mechanisms on the syncytiotrophoblast microvillous membrane (MVM) and demonstrates the expression of xCT and the Maxi chloride channel in the human placenta, the activity of which may be regulated by oxidative stress. Human term placental cotyledons were perfused with 58 nM 14C-glutamate in the maternal circulation. To stimulate exchange, 16 µmol boluses of glutamate, the antioxidant N-acetylcysteine (NAC), glutamine, taurine and serine were perfused into the maternal circulation. Volume regulated glutamate efflux was investigated by perfusing 50 mM urea into the maternal circulation and adding 50 mM urea to BeWo cells. Western blotting determined xCT expression in human placenta. Xenopus laevis oocytes were used to investigate NAC transport by xCT, by expressing human xCT-GFP/4F2hc. HEK293 cells were transfected with xCT-GFP/4F2hc and incubated with 14C-glutamate, with/without cystine (30-300 μM), NAC (30-3000 μM), glutamate (1 mM) and quisqualate (10 μM) to inhibit xCT mediated uptake. Glutamate efflux data are presented as median and interquartile range and were analysed using a Wilcoxon signed rank test. Maxi chloride channel perfusion data were analysed using a Mann-Whitney U test. Xenopus oocyte/cell culture 14C-glutamate efflux data are presented as mean and SEM and analysed using a one-way ANOVA with a Dunnett’s posthoc test whereby the efflux of 14C-glutamate was compared to control (buffer alone). xCT protein was localised to the MVM of the syncytiotrophoblast (n=4 blots, 45 μg protein). In placental perfusions, glutamate efflux occurred in response to potential xCT substrate NAC (n=6, p=0.031). In Xenopus laevis oocytes expressing human xCT-4F2hc, glutamate (10 mM) and NAC (10 mM) but not glycine trans-stimulated 14C-glutamate efflux compared to buffer alone (n=6, p<0.001). In BeWo cells (n=3 experiments, p=0.001) and the isolated perfused placenta (n=12 experiments, p=0.047), addition of urea boli to the maternal circulation stimulated release of 14C-glutamate. However pre-treatment with the antioxidant NAC decreased urea mediated glutamate efflux from both BeWo cells (p<0.05) and the placental perfusions (p=0.018). This study demonstrates glutamate efflux from the MVM of human placental syncytiotrophoblast by the transporter xCT and a volume regulated mechanism, likely to be the Maxi chloride channel. The finding that the antioxidant NAC inhibits volume regulated glutamate release suggests that Maxi chloride channel function may be regulated by oxidative stress status. As xCT appears to transport NAC, it is possible that Maxi chloride channel function is thus indirectly regulated by xCT activity.