On November 29, 1999, the French Institute for Public Health Surveillance (InVS) was informed by the National Reference Center for Salmonella and Shigella (CNRSS) of an increase, since the beginning of November, in human isolates of Salmonella Typhimurium reported by hospital and private clinical laboratories (LABM) in the Alpes-de-Haute-Provence department (04). Thirteen human strains had been isolated in this department, and this number—compared to the expected number (<1 strain) for this period and this department—was significantly higher. No cluster of cases had been reported to the CNRSS for this period and this department. An epidemiological investigation was launched in collaboration with the Departmental Directorate of Health and Social Affairs (DDASS) and the Southeast Interregional Epidemiology Unit to confirm the epidemiological nature of this phenomenon, identify the vehicle and source of contamination, and propose appropriate control measures. Initial findings from the epidemiological investigation indicated that several cases had occurred among patients while they were staying in medical-social institutions (IMS = hospitals, nursing homes) and suggested ground beef as a possible vehicle of contamination. (R.A.).