To determine which symptoms characterized isoproterenol-induced panic attacks, we analyzed the presence of panic attacks in 54 panic disorder patients who panicked, 24 patients who did not panic, and 37 controls who did not panic during isoproterenol infusions. The increases over the baseline of the symptoms shortness of breath and fear of going crazy were highly associated with panicking patients when compared to nonpanicking patients and nonpanicking controls. The increases of the symptoms trembling and shaking, generally nervous, and fear of going crazy were highly associated with patients when compared to controls. The possibility of a cognitive theory of panic attacks is discussed.