Marked increases in anxiety-like responses to stress occur during pregnancy. Considerable evidence indicates that the basolateral region of the amygdala (BLA) plays an important role in mediating these types of responses. Given the crucial inhibitory influence of GABA on excitatory glutamatergic activity in the BLA, we hypothesized that decreased GABAergic activity in this region may underlie the increased anxiety associated with pregnancy. In vivo microdialysis was used to sample extracellular GABA before and after 30 min of restraint stress. While there was no detectable effect of restraint on extracellular GABA concentrations, basal GABA levels were significantly decreased in pregnant rats compared with either virgin females or males. We suggest that the alterations in anxiety-like behavior that occur during pregnancy may be associated with decreased basal GABA in the BLA.