BergströmB. The effect of sleep loss and threat‐induced stress upon tracking.Scand. J. Psychol., 1972,13, 54–60.‐18 conscript soldiers were divided into z matched groups and trained on a missile‐type tracking task for 6 hrs. The experimental group was deprived of sleep for 75 hrs and both groups were then subjected to stress induced by electric shocks. Tracking performance was unaffected by sleep loss, probably due to the short duration of each trial. Performance under stress deteriorated in the control group but not in the experimental group. Heart rate decreased gradually under sleep loss but rose markedly under stress, and more so in the control group. Although somewhat inconsistent, the findings indicate that the effects of threat and sleep loss oppose each other by over‐arousing and de‐arousing,