Extracellular glutamate levels were measured by microdialysis in the prefrontal cortex (PFC) of anaesthetised rats in response to a short, experimenter-provoked mechanical movement of the animal head. Movement caused significant, nerve impulse-independent elevations of glutamate levels (maximum increase, 300+/-30% of baseline). This study reveals a possible artifact in the measurement of extracellular glutamate concentrations by microdialysis and suggests that, in awake animals, treatments associated with stimulation of motor activity can cause non-specific efflux of glutamate in the PFC.