A guidance document entitled "Recommended method for the establishment of Acceptable Operator Exposure Levels" has been prepared within the EU 5th Framework program. The paper describes the main outcomes of the project and the issues that apply particularly to agricultural workers and bystanders and the difficulties in developing an agreed uniform approach. The scientific basis of the process is discussed, to be used by the European Commission and Member States when making decision about the inclusion of an active substance in Annex 1 of Directive 91/414/EEC.