The present study explored anxious apprehension in panic disorder patients and controls in two threat conditions, darkness and threat of shock. Autonomic arousal and startle eyeblink reflexes were recorded in 26 panic disorder patients and 22 controls during adaptation, a safe condition, threat of shock, and darkness. Exposure to darkness resulted in a clear potentiation of the startle reflex. Panic patients but not controls responded with an increase in heart rate that was positively related to severity of agoraphobic avoidance. Threat of shock resulted in a startle potentiation that tended to be stronger in panic patients without comorbid depression than controls and attenuated in those patients who suffered from severe depression. These data suggest that only panic patients without depression belong to the fear disorders spectrum whereas panic patients with comorbid depression might rather belong to the distress disorders profile.