Night sleepiness in two groups of student volunteers who stayed awake for one night was assessed at standardized time (22:00, 01:00, 04:00, 07:00) by the Stanford Sleepiness Scale (SSS). One group (N=21) chewed the chewing gum from midnight until the end of the experiment in the morning, while the other group (N=43) was not chewing at all. The results show that both groups at the initial assessment at 22:00 were not sleepy, with similar SSS scores. Sleepiness in both groups appeared after midnight, worsening towards the morning. The students who were chewing from midnight assessed their sleepiness as lower than the students who were not chewing, which was more marked at 01:00 and 04:00. In the group of medical professionals, nurses and technicians, sleepiness was assessed by SSS in a routine night shift when they, according to their own experience, had the most difficulty overcoming it. Immediately after the assessment they chewed the chewing gum (N=60) or stood/walked (N=27) for 15 minutes. At the end of the fifteenth minute, they assessed their sleepiness again. After 15 minutes of treatment both groups of medical professionals assessed their sleepiness as relieved, with a lower SSS score, more markedly in the chewing group. The obtained results seem to indicate that chewing may alleviate sleepiness in professionals and nonprofessionals who stayed awake through the night.