Changes in wakefulness before and after exposure to carbohydrate intake were tested in 30 test persons. Changes in wakefulness were tested via EEG and subjective estimates. The intakes consisted of 400 ml glucose, 250 kcal (GI 100), 400 ml fructose, 209 kcal (GI 20), and 400 ml water. The study has indicated that intake of fructose, glucose and water had a similar stimulating effect on wakefulness in drowsy subjects immediately after intake. Our results also indicate that intake of fructose can lead to a delay in the development of drowsiness. Compared to water, a 20-30 minutes delay of the point in time when high-degree drowsiness developed, took place. There was no significant difference between glucose and water.