The dynamic interplay between reflexive and controlled determinants of behavior is one of the most general organizing principles of brain function. A powerful analogue of this interplay is seen in the antisaccade task, which pits reflexive and willed saccadic mechanisms against one another. Event-related functional magnetic resonance imaging of the human brain showed greater prestimulus preparatory activity in the pre-supplementary motor area before voluntary antisaccades (saccades away from a target) compared with reflexive prosaccades (saccades to a target). Moreover, this preparatory activity was critically associated with reflex suppression; it predicted whether the reflex was later successfully inhibited in the trial. These data illustrate a mechanism for top-down control over reflexive behavior.