Bifidobacteria are the predominant members of the infant gut, colonize adults to a lesser extent, and are recognized as beneficial microbes. Various bifidobacterial species produce ��-aminobutryic acid (GABA), the chief inhibitory neurotransmitter in the mammalian central nervous system. It is postulated that in order to produce GABA, the bifidobacterial genome must contain the gadB and gadC genes which encode a glutamate decarboxylase and a glutamate/GABA antiporter, respectively. Once exported by GadC, GABA is absorbed and transported systemically throughout the host. We hypothesize that specific dietary oligosaccharides will modulate bifidobacterial production of GABA due to varying intracellular concentrations of glutamate. To test this, 33 bifidobacterial strains were screened for GABA production via reverse phase HPLC. Interestingly, 10 strains contained both gadB and gadC genes, but only 8 strains produced detectable GABA in vitro. To further elucidate the extrinsic factors influencing GABA production, strains were subjected to different dietary components. Specifically, lactose and the dietary oligosaccharide FOS were evaluated for the ability to promote biosynthesis of intracellular glutamate and thus potentially GABA. Understanding the relationship between diet, bifidobacterial physiology, and GABA production may inform dietary interventions to modulate this neurotransmitter in vivo.