We and others have previously reported that N-methyl-D-aspartate (NMDA) induces nitric oxide (NO) release from the rat cerebral cortex in vivo. It is crucial to determine if this phenomenon also exists in human brain tissue. In this study, we investigated the interactions of NMDA and NO in human primary neocortical cell cultures obtained from elective abortions. Extracellular NO concentration was monitored through Nafion- and porphyrine-coated carbon fiber electrodes, which have previously been demonstrated sensitive and selective responses to NO. We found that local application of NMDA induced NO release from neocortical neuron-enriched cultures but not from glial cultures. Pretreatment with NG-nitro-L-arginine methyl ester hydrochloride (L-NAME), a nitric oxide synthase inhibitor, or MK801 significantly attenuated NMDA-induced NO overflow. This is the first time, to our knowledge, that extracellular NO concentration evoked by exogenous NMDA has been directly measured from the fetal human cortical neurons.