The effects of sympathetic arousal level on habituation and below-zero habituation of the skin conductance component of the orienting response (OR) were investigated in an experiment employing 60 subjects. Threat of shock was used to increase the arousal level of one group of subjects. These subjects were compared to a group that was not threatened by shock. Half of the subjects in each group received below-zero habituation training; the other half received no below-zero habituation. Results indicated that threat of shock significantly increased tonic skin conductance level. This increase in physiological arousal level was associated with decreased habituation of the OR. Moreover, increased arousal level and below-zero habituation training significantly affected the subsequent reappearance of the OR to a novel, dishabituating stimulus. The results of this study clearly demonstrate that physiological arousal level significantly affects the habituation and below-zero habituation processes.