In August 2003, a heat wave with exceptional health consequences struck France. This health crisis led to massive strain on the emergency care system and a sharp rise in mortality. The first noticeable consequence was the saturation of the emergency care system, while public health surveillance services and networks, which lacked early warning indicators, failed to respond as expected. This health crisis necessitated a review of the health surveillance systems designed for alert purposes that were available in France at the time. It also prompted the French Institute for Public Health Surveillance to launch a network of emergency services aimed at identifying health situations requiring an appropriate public health response and ensuring the measurement of the impact of epidemics and anticipated events. (R.A.)