With the aid of microiontophoretic techniques the action of caroverine, a quinoxaline-derivative, was tested on the receptor-linked depolarisation of the subsynaptic membrane of cochlear afferents. This membrane can be depolarised by the afferent transmitter agonist glutamate, mediated by NMDA and non-NMDA receptors and by acetylcholine, one of the different transmitter substances, released physiologically on axodendritic efferent synapses. Caroverine antagonized the membrane response to glutamate in an enduring but reversible manner. In contrast, the drug exhibited no effect on the depolarising action of acetylcholine. Therefore, the pharmacological profile of caroverine corresponded to the action of selective glutamate receptor antagonists. Since glutamate is likely to be the major mediator of neurotoxicity in the central nervous system, the selective glutamate-antagonism of caroverine is of particular interest, due to its putative neuroprotective competence. Caroverine is currently available clinically in some countries as a spasmolytic drug. Following these results it is proposed to test the drug for clinical efficacy in putatively glutamate-induced, excitotoxic disorders of the brain.