September 11 brought increased awareness that even the threat of chemical and biological terrorism can overwhelm this country's health care system. Belief in exposure to toxic agents, even when none is documented, is not uncommon in crisis and merits vigilant health care evaluation and services. This study examined risk factors (demographics, physical symptoms, clinical diagnosis, exposures, and health status) for belief in exposure to potential terrorist agents (nerve or mustard gas) using a large sample of Gulf War veterans who reported belief in exposure to nerve or mustard gas. We found that females, nonwhites, and those who were older (age 32 to 61 years) were more likely to report exposure. When adjusting for demographics and military service, these veterans reported more exposures (nonnerve or mustard gas) to potentially toxic agents and traumatic events (odds ratio [OR], 6.80; p<.001), reported more physical symptoms during the Gulf War (OR, 2.38; p<.001), were more likely to be diagnosed with a mental disorder (OR, 1.72; p<.001), and reported poorer current health status (OR, 3.47 to 1.22; p<.001). Not unlike previously reported studies of disasters, traumatic exposures, or risk exposures, belief in exposure to toxic agents suggests that certain people are at a greater health care risk. This knowledge will aid in better responding to rapid demands that may be placed on our health care delivery systems in times of potential terrorist activity.