Agricultural biotechnology has generated concern over the risk of producing new invasive species or exacerbating current weed problems. In this paper, we introduce the regulatory context for assessing invasiveness of genetically engineered organisms in the United States and review the evidence presented by companies arguing the deregulation of particular transgenic crops. The context of invasion ecology is then used to discuss the nature of acceptable evidence for a finding of 'no risk',: we focus in particular on the role of experimental data. We review recent experiments designed to assess the risk of gentically engineerred crops, including our own work with oil-modified canola Brassica napus, and offer guidelines for the design and interpretation of such experiments.