When examining headache sufferers' reactivity to stress, few studies attend to differing characteristics of the environment. In this study, we evaluated the influence of the clarity/ambiguity and positive/negative valence of an event on subjects’ physiological and psychological reactivity. Migraine (n=30), tension (n=39) and control (n=35) subjects participated in a laboratory experience in which they had to practice and then deliver a news story to a videocamera (similar to a newscaster on television). During this experience, they received performance feedback and were instructed to try to use the information to improve their performance. In reality, this feedback was noncontingent, with subjects semirandomly assigned to either a positive, negative, or ambiguous feedback condition. Physiological and psychological measures were collected prior to this experience, during an anticipation or practice period prior to the newscast, and during a recovery period following the delivery of the news story. Results suggested that tension subjects might not attend to information from their environment when assessing, responding, or reevaluating potentially stressful events: relying instead on more global beliefs or attributions. Results also indicated that migraine might be associated with a prolonged cardiovascular response (ie, delayed recovery) following a stressful experience.