[en] Prior to 1998, the development of RODOS, a decision support system designed for the management of nuclear emergencies, had been carried out almost entirely by research scientists and engineers. The end-users/operators had little or no input into this development. To redress this situation, the RODOS Users Group (RUG) was established in 1998 under a Concerted Action Contract between the European Commission and STUK. The main objectives of this group were to encourage the emergency management community to use such a system, to provide a forum for end-users to share their experience in the use of such systems and to provide feedback from the end-users to the model and system developers in regard to operational problems and required improvements. The contract, which commenced on 1st September 1998, was for a period of two years. During this period, RUG established a www homepage, planned and performed two nuclear accident exercises and held four meetings. Technically the Web page operated very well. State-of-the-art Internet technology provided an efficient communication channel at low cost. The membership of the RUG was, however, too low to maintain a lively and ongoing discussion in parallel with the RODOS project Web page. This experience would suggest that it might have been better to have operated a Web page for RUG on the RODOS project Web-site rather than an independent RUG Web-site. Exercises based on fixed accident scenarios proved to be an appropriate means of highlighting issues that needed to be discussed between users and developers and to stimulate and motivate the end-users to maintain and further develop the system. Such exercises also promoted further activity in the field of emergency management. The organisation and administration of realistic exercises are time consuming, laborious and expensive. It is therefore very important that the maximum benefit is achieved from such exercises. The use of analytical evaluation methods could be better employed for assessing an exercise and analysing the results. It would be useful in this context to formulate a framework that could provide scientific levels of merits and guarantee the full documentation of the work and effort invested. The workload in designing future exercises for RODOS could be reduced by taking all opportunities to use RODOS in international exercises. Users with expertise and a responsibility in the field of emergency management have to be familiar with the relevant models used in the decision support system (DSS). They have also to be aware of the level of reliability of the calculated results and the limits and conditions applying to the model predictions. It is therefore essential that good co-operation exists between end- users and the R and D community developing the system. The RUG provided a forum for the end-users through which they could communicate their requirements to the developers, receive advice and demonstrations of the latest additional features to the system. It is seen essential that the end-user can contribute to the development of models used in RODOS and other DSSs, and perhaps in the future, become more involved in the R and D aspects of these systems. (orig.)