In vivo electrochemistry has been a valuable tool in detecting real time neurochemical changes in extracellular fluid. Absolute selectivity has been difficult to achieve previously, but we report here a carbon fiber electrode and measurement technique which is specific for one oxidizable species: ascorbic acid. Ascorbic acid is highly concentrated in extra- as well as intracellular brain spaces, and appears to undergo dynamic changes in response to a variety of physiological and pathophysiological circumstances. Recent studies have implicated glutamatergic mechanisms which give rise to extracellular changes in brain ascorbate, and we confirm and extend these observations. Preliminary studies, directed towards examining ascorbic acid as an index and/or result of hypoxia, spreading depression, and seizure activity, have been undertaken and the results are reported herein.