The aim of this experiment was to test the effect of brief exercise on the concentration of plasma hypocretin-1, a peptide that regulates many physiological variables. Blood samples were collected from participants (men, n=6) before (time 0 min) and after (times 15 and 30 min) a cycle ergo meter exercise at 75 W for 15 min. The physical exertion was monitored by heart rate registration. The exercise causes a significant increase in plasmatic hypocretin-1, in association with an increase of hearth rate. These results are the first demonstration, which indicates that plasma hypocretin-1 is involved in the reactions induced by physical activity.