A major challenge in the elucidation of brain neurotransmitter events in vivo in the laboratory and in the operating room has been the development of methods to record neurotransmitters in the CNS on a second-by-second time scale. Microdialysis methods have been widely employed but are limited due to their inherent slow sampling rates (1-20 min) and poor exchange (∼10-20%) of neurotransmitters. We have developed an enzyme-based ceramic microelectrode array (MEA) for 2Hz measures of tonic (resting) and phasic (spontaneous bursts or stimulated) release of neurotransmitters. We have used the most recent designs for reproducible, sensitive, selective and rapid measures of L-glutamate and other neurotransmitters in rats, mice and monkeys. In conjunction with Ad-Tech Medical Instruments Inc., we have recently developed a new MEA design for nonhuman primate and human recordings that lays the foundation for potential use of this technology during neurosurgery for intra-operative chemical diagnostics.