Objective. - Can causal relationships be established between negative affect (NA) and headaches, and noise (N) and headaches? Do NA and N interact to cause headaches? Do NA and N cause headaches by means of the same or different physiological mechanisms? Are the answers to these questions a function of diagnostic status? Background. - A functional model of chronic headaches has been proposed that seeks to understand the variance in headaches by focusing on the controlling variables, that is, the antecedents and consequences. This study is one in a series investigating the immediate antecedents of headaches, namely the trigger factors. Design. - Twenty-four subjects with migraine and 44 subjects with tension-type headache were randomly assigned to one of four experimental conditions defined by the presence or absence of two antecedent challenges, a stressor (S) designed to induce NA and N. Methods. - The S challenge consisted of difficult-to-solve anagrams accompanied by failure feedback. The N challenge consisted of 50 dB of white N. Laboratory sessions were divided into adaptation, baseline, challenge, and recovery phases. Responses were measured in terms of headache intensity ratings, forehead electromyographic activity, heart rate, blood pressure, and temporal pulse amplitude (TPA). Results and Conclusions. - Both NA and N precipitated headaches. These two factors did not interact in triggering headaches. Headaches induced by N were associated with elevated TPA but headaches induced by NA were not associated with significant physiological changes. Diagnosis was not related to any of the outcomes.