Following the heat wave of summer 2003, the French Institute for Public Health Surveillance launched several studies: two case-control studies to examine risk factors for mortality among older adults, both at home and in care facilities, during the heat wave; and a study of nine French cities to assess the health impact of photochemical pollution and temperature. Furthermore, to prevent the consequences of a new heat wave, an operational alert system for the summer of 2004 was developed, based on excess mortality from all causes that could be linked to temperature. As part of the National Heat Wave Plan of the Directorate General for Health, this system was designed to alert public authorities three days in advance of the possible occurrence of a large-scale epidemic linked to a heat wave. Following its first year of operation, it will be evaluated and improved for the summer of 2005.