Anxiety sensitivity (AS) has been defined as the fear of anxiety and anxiety-related sensations, and evidence suggests that AS plays an important role in the psychopathology of panic. It is entirely unclear whether the relation between AS and panic should be attributed to one (or more) of the AS group factors, the general AS factor, or to factors at both levels of the AS hierarchy. The authors reanalyzed data presented earlier by R. M. Rapee, T. A. Brown, M. A. Antony, and D. H. Barlow (1992) to tease apart the contributions of the different levels of the AS hierarchy to fear responses to hyperventilation and 5.5% carbon dioxide challenges. The results demonstrated that AS-Physical Concerns is the only one of the three AS group factors that contributes to relations with fear responses to these two challenges. However, AS-Mental Incapacitation Concerns had a stronger positive linear association with depressed mood than did AS-Physical Concerns.