The objective of this session was to discuss information that is relevant in determining whether a potential hazard can occur and at what frequency. This session targeted setting the background for a more in-depth discussion on exposure assessment for GM crops by identifying key factors such as gene flow, frequencies and factors that affect them, as main components of exposure. Gene flow is a particularly complex subject, and estimating a frequency requires a great deal of information. Information on gene flow can be gathered using models (based on what is already known from the traditional crop), empirical data from fields, as well as molecular information, to understand gene flow from an historical perspec-