Due to the terrorist attacks of 9/11 and the anthrax letters of a few weeks later, the concept of dual use has spread widely in the life sciences during the past decade. This article is aimed at a clarification of the dual use concept and its scope of application for the life sciences. Such a clarification would greatly facilitate the work of policymakers seeking to ensure security while avoiding undesirable interventions of government in the conduct of science. The article starts with an overview of the main developments in life sciences in relation to dual use. This is illustrated by discussions on synthetic biology and dual use. The findings lead to a reconsideration of the dual use concept. An area in need of further attention is to what extent threats and intentions should have impact on the definition of dual use. Possible threats are analyzed against the background of the phenomenon of securitization of health care and life sciences: considering these sectors of society in security terms. Some caveats that should be taken into account in a dual use policy are described. An acceptable, adequate and applicable definition of the dual use concept could help researchers, universities, companies and policy makers. Such a definition should build upon, but go beyond, the view developed in the influential Fink-report, which concentrates on the so-called 'experiments of concern', e.g. experiments that enhance the virulence of pathogens (National Research Council of the National Academies 2004) It will be argued that-in addition to these more technical aspects-a definition of dual use should include the aspect of threats and intentions.