Striatal quinolinate lesions mimic many of the neuropathological characteristics of Huntington's disease. This excitotoxicity is mediated by combined activity of N-methyl-n-aspartate and metabotropic glutamate receptors (mGluRs). Using recently developed phenylglycine derivatives, (S)-4-carboxy-3-hydroxyphenylglycine ((S)-4C3HPG) and (+)-α-methyl-4-carboxyphenylglycine ((+)-MCPG), we investigated the role of the different sub-classes of mGluRs in the in vivo excitotoxic process. (S)-4C3HPG (500 and 1000 nmol), co-injected with quinolinic acid, significantly reduced lesion volumes by 52 and 89%, respectively, whereas the same doses of (+)-MCPG had no effect on lesion size. The differential actions of these two drugs at Group 1 and Group 2 metabotropic receptors may explain their differential effects. These observations confirm the important role of mGluRs in excitotoxicity and identify them as promising targets for intervention. © 1995.