Slices of rat cingulate cortex, when incubated in magnesium-free medium, produce spontaneous epileptiform spikes. Here it is demonstrated that the metabotropic glutamate receptor (mGluR) agonists +/- trans-1-amino-cyclopentane-1,3-dicarboxylic acid (+/- Trans-ACPD), IS3R-ACPD and quisqualic acid (quis) can reduce the frequency of these bursts in a concentration-dependent manner. The IC50 values were 16, 12 and 26 microM, respectively. The low concentrations of +/- trans- and IS3R-ACPD used, plus the lack of NMDA antagonism shown by these compounds, suggest that the effect may be via a presynaptic reduction in glutamate release. The relative potency of the agonists IS3R-ACPD > Trans-ACPD > quis would seem to suggest that the mGluR1 receptor is not involved.