In case of a terrorist's threat to release nuclear or radioactive material methods and procedures are needed for fast search and, after detection, identification of the substance. For searching the German Fraunhofer-INT in Euskirchen has a car at its disposal, which is equipped with very sensitive detectors suitable for a first identification of the material. Advanced measurements are performed with portable detectors of high energy resolution or by scanning of buildings or objects with a gamma camera. Initially such material may be stored under water in preparation for an attack. In this case we have a special sensor available for detection and subsequent identification. In case of no suspicious material being detected with all these passive methods, even though a well-founded suspicion exists, active methods will be employed. Therefore neutron interrogation is briefly presented. With all these techniques it is possible to determine the presence of radioactive or fissionable materials, as well as, within certain limits, type and quantity of material. Hence information will be gained on the possible risk potential and, by actions taking radiological aspects into account, recommendations can be given on further actions to be taken.