Several recent studies have demonstrated a neuromodulatory role for endocannabinoids via their ability to act as retrograde inhibitors of synaptic neurotransmission. We utilized the functional hyperemic response to controlled whisker stimulation to determine whether endogenous cannabinoids modulate synaptic transmission within the primary somatosensory cortex of rats. As previously demonstrated, whisker-stimulation resulted in a robust hyperemic response measured using laser Doppler flowmetry within the whisker barrel cortex. Administration of the CB(1) receptor antagonist, SR141716 (1 mg/kg i.v.), significantly potentiated the functional hyperemic response to whisker-stimulation, while having no effect on basal blood flow within the whisker barrel cortex. These data suggest that suppression of endogenous cannabinergic neurotransmission results in increased cortical activity in response to physiological sensory stimulation.