The risk of bioterrorism for plant diseases can be assessed through general probabilistic models. A simple but useful model for risk can be written of the form: I*E*S*(1-C), in which I is the probability of introduction of a pathogen, E is the probability of initial establishment (primarily dependent on the environment), S is the probability of disease spread, and C is the probability of successful confinement, eradication or control. With bioterrorisim, I can be considered equal to 1, since we are, by definition, dealing with deliberate introduction of pathogens. The other terms can vary greatly, however, based on the properties of the pathogen and host. E can be determined using the ecoclimate index method of Sutherst and Maywald or similar macro-environmental model, and S can be determined with the basic reproductive number (Ro) for epidemic development (i.e., the number of new infections arising from each initial infection). Using this risk-model approach, the potential for bioterrorism with plant pathogens will be explored under various scenarios.