Since September 11, 2001, concern about potential terrorist attacks has increased in the United States. To reduce morbidity and mortality from outbreaks of illness from the intentional release of chemical agents, we examine data from the Toxic Exposure Surveillance System (TESS). TESS, a national system for timely collection of reports from US poison control centers, can facilitate early recognition of outbreaks of illness from chemical exposures. TESS data can serve as proxy markers for a diagnosis and may provide early alerts to potential outbreaks of covert events. We use 3 categories of information from TESS to detect potential outbreaks, including call volume, clinical effect, and substance-specific data. Analysis of the data identifies aberrations by comparing the observed number of events with a threshold based on historical data. Using TESS, we have identified several events of potential public health significance, including an arsenic poisoning at a local church gathering in Maine, the TOPOFF 2 national preparedness exercise, and contaminated food and water during the northeastern US blackout. Integration of poison control centers into the public health network will enhance the detection and response to emerging chemical threats. Traditionally, emergency physicians and other health care providers have used poison control centers for management information; their reporting to these centers is crucial in poisoning surveillance efforts.