Empirical research has demonstrated that the Anxiety Sensitivity Index (ASI) contains three separable factors and that ASI total scores are useful in predicting response to physiological challenge procedures. Little is known, however, of the predictive capability of the ASI factors. This study investigated the utility of the three factors of the ASI compared to ASI total scores and the STAI-T, a more general measure of trait anxiety, in predicting response to hyperventilation. As expected, the ASI total score was a significant predictor of response to hyperventilation, while the STAI-T was not. Using multiple regression, when the physical concerns factor was entered first, the social concerns and mental incapacitation factors of the ASI were not significant predictors of response to hyperventilation. Furthermore, when the physical concerns factor was entered into a regression equation followed by the remainder of the ASI items, only the physical concerns factor remained a significant predictor of response to hyperventilation. These results suggest that while response to physiological challenge procedures is predicted by ASI total scores, it may be best predicted by the physical concerns factor, and that the mental incapacitation and social concerns subscales do not play key roles in predicting response to physiological challenge procedures.