Saccades elicited by suddenly appearing targets show a broad distribution of reaction times. This may depend on variations in the subject's state of preparation before target onset. To test this hypothesis, we recorded scalp event-related potentials from eight human subjects to investigate whether differences in saccadic reaction times (SRTs) are related to differences in cortical slow potentials prior to target onset. Compared with trials with medium SRTs (180-230 ms), trials with fast SRTs (130-180 ms) were found to be preceded by a more negative slow potential and trials with slow SRTs (230-280 ms) were found to be preceded by a more positive slow potential. These results support the hypothesis that cortical activation prior to target appearance influences SRTs.