In 1989, a Radiological Transmission and Early Warning System (SYTAR) came into being in order to harmonize radioactivity surveillance methodologies and furthermore to trigger off an alert throughout the networks whenever an unusual degree of radioactivity is detected. SYTAR is a remote permanent system linking up a national electronic access and the radiation protection services of nuclear facilities located on the mainland. The structure of the network are particularly presented in the framework of a drill organized on october 1991 in the south-east of France. During this drill, an accident was simulated on a ghost nuclear power plant located in the Cadarache Nuclear Center. A large number of samples were taken from filtered aerosols, soils, grass, milk, vegetables, food stuff; they were contaminated with Caesium 137 and Iodine 131 before to be sent to laboratories for measurements. The results of measurements were transmitted to the actors of the drill using SYTAR network. They permit to determine the exclusion area, the radiological impacts and counter-measures. (author).