The surveillance of genetically modified organisms (GMO) dispersal is a new challenging task in environmental monitoring.  Web-based geoinformation systems (WebGIS) are tools for the harmonisation of monitoring methods, network design and data handling in the framework of GMO-monitoring data.  Furthermore, WebGIS can be used for serving report duties, for planning GMO-monitoring or as data base for statistical analyses and dispersal models.  We developed a WebGIS GMO Monitoring and integrated site-specific data from appropriate environmental monitoring networks and surface maps allowing for the description of the environment of the monitoring sites in terms of, e.g., land use and climate or altitude above sea level.  We used platform independent Open Source-software.  The WebGIS considers standards released by the Open Geospatial Consortium (OGC) and the International Organisation for Standardisation (ISO) to ensure interoperability between web mapping services (WMS) located all over the world.  Projects like INSPIRE (Infrastructure for Spatial Information in Europe) or PortalU use these standards as well.  The WebGIS GMO Monitoring offers tools for visualisation, spatial and logical queries as well as interactive data processing tools.