Many people affected by debilitating neuromuscular disorders such as amyotrophic lateral sclerosis (ALS), brainstem stroke, or spinal cord injury, are impaired in their ability to, or even unable to, communicate. A Brain-Computer Interface (BCI) uses brain signals, rather than muscles, to re-establish communication with the outside world. One particular BCI approach is the so-called "P300 matrix speller" that was first described by Farwell and Donchin in 1988. It has been widely assumed that this method does not depend on the ability to focus on the desired character, because it was thought that it relies primarily on the P300 evoked potential and minimally if at all on other EEG features such as the visual evoked potential (VEP). This issue is highly relevant for clinical application of this BCI method, because eye movements may be impaired or lost in the relevant user population.This study investigated to what extent performance in a "P300" speller BCI depends on eye gaze. We evaluated the performance of 17 healthy subjects using a "P300" matrix speller during two conditions. In one condition ("letter"), the subjects focused their eye gaze on the intended letter, while in the second condition ("center"), subjects focused eye gaze on a fixation cross that was located in the center of the matrix.The results show that the performance of the "P300" matrix speller in normal subjects depends in considerable measure on gaze direction. They thereby disprove a widespread assumption in BCI research, and suggest that this BCI might function more effectively for people who retain some eye-movement control. The applicability of these findings to people with severe neuromuscular disabilities (particularly in eye-movements) remains to be determined.