The present study investigated the ability of mGlu (metabotropic glutamate) receptor to modulate dopamine release in the striatum of freely moving rats assessed using the microdialysis technique. The group I and II mGlu receptor agonist (1S,3R)-ACPD (1-amino-cyclopentane-1,3-dicarboxylate; 1-3 mM) increased dopamine release (367% of basal levels) which was prevented by the non-selective mGlu receptor antagonist, (+)-MCPG (alpha-methyl-4-carboxyphenylglycine; 10 mM). The group I mGlu receptor agonist, DHPG (3,5-dihydroxyphenylglycine; 0.3-1 mM), also increased dopamine release (maximum increase 229%) which was also antagonised by (+)-MCPG (10 mM). In contrast, the group II mGlu receptor agonist, DCG-IV (2-(2,3-dicarboxycyclopropyl)glycine; 3-50 microM), induced a more modest increase in dopamine release (156% of basal levels). Combined administration of DHPG (1 mM) and DCG-IV (50 microM) maximally increased dopamine release by 252% of basal levels which was antagonised completely by (+)-MCPG (10 mM). Such findings indicate that group I (and possibly group II) mGlu receptors facilitate rat striatal dopamine release in vivo.