Bipolar affective disorder (BPD, manic-depressive illness) is a common, severe, chronic and often life-threatening illness. Increasingly, it is being recognized that it is the depressive phase of the illness, which contributes much of the morbidity and mortality. To date, only a few of the available somatic treatments have been proven to be effective for the acute phase of bipolar depression. Thus, there is a clear need to develop novel and improved therapeutics for bipolar depression. Recent preclinical studies suggest that antidepressants may exert delayed indirect effects on the glutamatergic system. Clinical data suggests that glutamatergic modulators may have antidepressant effects in humans. We first tested the glutamatergic modulator riluzole, an inhibitor of glutamate release and enhancer of glutamate reuptake in astrocytes and found it to have antidepressant properties in patients with treatment-resistant major depression and bipolar depression. In a recent study, we found that a single intravenous dose of the non-competitive NMDA antagonist ketamine produced a rapid and relatively sustained antidepressant effect in patients with treatment-resistant major depression. A recent report found that the Beta-lactam antibiotic ceftriaxone increased uptake of glutamate via increased GLT1 function (Rothstein et al 2005) and had antidepressant-like effects in animal models (Mineur et al 2006). Together, these data suggest that the glutamatergic system may play a role in the pathophysiology and treatment of depression, and that agents which more directly reduce glutamatergic neurotransmission may represent a novel class of antidepressants.