At the site of the Research Center Jülich (FZJ), open radioactive substances are used which, despite careful handling, can reach the environment in a small fraction with the filtered exhaust air and the treated wastewater. Monitoring of the environment for radioactivity is therefore indicated and prescribed in conditions attached to the various nuclear licenses issued by the Research Center and Jülich Entsorgungsgesellschaft für Nuklearanlagen mbH (JEN). Such monitoring serves to detect radioactive contamination in the environment and to preserve evidence. Furthermore, it is the basis for a radioecological evaluation of the emissions and thus serves to protect the population. The basis of the measurement program for immission monitoring practiced at Jülich is the "Guideline for Emission and Immission Monitoring" [REI].