After the Chernobyl reactor accident in 1986 many European Governments decided to improve their organisation and infrastructure for the management of nuclear emergencies. In the Netherlands this resulted in an update of the national organisation for emergency planning and response, and a series of technical facilities for the collection and presentation of technical information. Of all facilities available at present, the National Radioactivity Monitoring network (NRM) forms a key element. An overview is given of the present set-up and experiences obtained with the NRM since 1990 are described. Special emphasis is given to events which have led to automatic 'early warnings'. Of these events, categorised in groups according to origin, malfunction of equipment has the largest share (45%), but in general easy to diagnose. Although local human activities did account for only 25% of the warnings, they caused the most concern. Fluctuations of the natural background of ambient dose rate due to rainout or washout of radon progeny led to a warning message on only two occasions. The actual cause of the remaining 25% of the received warning messages could not be concluded with certainty.