In the present study, the effects of the γ-hydroxybutyrate (GHB) analog GET73 on hippocampal glutamate transmission have been evaluated by an approach combining in vivo microdialysis with the in vitro evaluation of tissue slices. The microdialysis results indicated that local perfusion (60 min) with 10 nM - 1mM GET73 increased extracellular glutamate levels in the CA1 region of the hippocampus of freely moving rats in a concentration dependent manner. In tissue slices from the rat hippocampus, GET73 (1 μM - 10 μM) did not affect L-[(3)H]glutamate uptake, whereas treatment with 1 μM GET73 significantly increased K(+)-evoked, but not spontaneous, glutamate efflux. The GHB analog did not affect the increase in glutamate efflux induced by 100 μM and 300 μM NMDA. In contrast, 500 nM GET73, a concentration at which it is ineffective alone, partially but significantly counteracted the increase in K(+)-evoked glutamate efflux induced by 100 μM CHPG, an mGluR5 agonist. When 500 nM GET73 was coperfused with 100 μM MPEP, it amplified the decrease in K(+)-evoked glutamate efflux induced by the mGluR5 antagonist. Interestingly, the increase in K(+)-evoked glutamate efflux induced by 1 μM GET73 was counteracted by coperfusion with a low (10 μM) concentration of MPEP, which by itself is ineffective. Finally, 500 nM GET73 did not affect the reduction of K(+)-evoked glutamate efflux induced by the mGluR2/3 agonist LY379268. These findings demonstrate that the GHB analog GET73 significantly affects glutamate transmission in the hippocampus, and its profile of action differs from that of its parent compound.