AcknowledgmentsThe authors would like to thank two anonymous reviewers for their comments on an earlier draft of the manuscript. AbstractThe proposition that chewing gum can improve alertness was investigated via both physiological and self-rated measures. The Pupillographic Sleepiness Test (PST) provided a measure of pupillary unrest (PUI); a physiological index of daytime sleepiness. Chewing gum reduced the extent of sleepiness as measured by both PUI and self-rated sleepiness. Specifically, in comparison with sham chewing and no chewing controls, the chewing gum condition significantly limited the increase in pupillary unrest following the 11-minute PST within a darkened laboratory: a finding indicating moderation of the daytime sleepiness increase for the chewing gum condition. In addition, there was some evidence that chewing gum (relative to the nochewing condition only) moderated the increase in a self-rated measure of sleepiness (Stanford Sleepiness Scale). However, there was no evidence that chewing gum moderated the decrease in self-rated alertness (Bond-Lader Visual Analogue Mood Scale). Although the precise mechanism underpinning the effect of chewing gum is unclear, the reduction in daytime sleepiness may be underpinned via heightened cerebral activity following the chewing of gum or the arousing effects of mint flavour.