Short-term effects of transcranial direct current stimulation (tDCS) on CBF were measured using arterial spin labeling (ASL) MRI. Results showed that anodal surface stimulation of the motor region was followed by an increase in gray matter CBF in that region. Conversely, CBF in the stimulated region following a cathodal stimulation decreased. There was no effect of sham stimulation on the CBF of the stimulated area. These findings may help forge a new path toward a better understanding of the neuro-physiological effects of tDCS in humans.