Syndromic surveillance has been developed in order to detect outbreaks of unusual infectious diseases such as severe acute respiratory syndrome (SARS) or anthrax at an early stage. Whereas the usual surveillance systems are based on established diagnoses and emergency department discharge data, syndromic surveillance uses preliminary outcomes and derived data such as absenteeism, prescription medication and requests for laboratory tests. Investigations abroad have indicated the potential ofsyndromic surveillance. In the Netherlands, the National Institute of Public Health and Environment (RIVM) is examining the feasibility of implementing syndromic surveillance.