A dose-dependent, saturable, and calcium-dependent release of gamma-[3H]aminobutyrate [( 3H]GABA) from cortical neurones and D-[3H]aspartate from cerebellar granule cells following stimulation by a range of L-enantiomers of neuroactive acidic sulphur amino acids has been demonstrated. Moreover, the sulphur amino acid-evoked release of the transmitter amino acids was found to be sensitive to the presence of both selective N-methyl-D-aspartate and quisqualate/kainate receptor antagonists. Following the recent demonstration of an endogenous location for several of the acidic sulphur amino acids and their excitotoxic involvement in several neuropathological states and coupled with the knowledge that many important CNS connections are still undefined as far as their excitatory transmitter or transmitters are concerned, the present findings are of immediate importance in the continued search for endogenous excitatory amino acid agonists in addition to glutamate and aspartate.