WHO Informal Working Groups on Echinococcosis were founded in 1985 and for 10 years, under the leadership of Prof. J. Eckert (Zurich, Switzerland), they contributed much to facilitate exchanges between interested scientists working in their respective areas. In 1995, the Veterinary Public Health Unit, at WHO, decided to modify the functioning of the Groups and to transform them into a single Group. The Working Group brings together all the scientists involved in research on Echinococcosis whatever their specialty, field of interest, or type of Echinococcosis studied. The aim of the Group is to establish international networks on relevant, up-to-date and/or important problems in Echinococcosis on the basis of i) international cooperation, ii) high scientific standards, and iii) accurate methodology. A Coordinator is designated by WHO and has a 4-year term. He/she is assisted by a Coordinating Board. This board is also proposed for a 4-year term, so that it can be regularly renewed. It, thus, will give an opportunity for closer association with the life of the Working Group to many scientists; the coordinator for the next term will be chosen from among the participants so that a continuity of action is ensured. The current networks deal with: "Standardization of the ultra-sound classification of hydatid cysts" (coordinator: C. Mcpherson); "Long-term follow-up of patients treated with PAIR" (coordinator: C. Filice); "Standardization of the staging/classification of patients with Alveolar Echinococcosis" (coordinator: P. Kern); "Vaccination of sheep for the prevention of Echinococcosis: pilot trials" (coordinator: M. Lightowlers); "Standardization of immunological tools for the detection of Echinococcus coproantigens in carnivores" (coordinator: P.S. Craig); "Educational material for Echinococcosis prevention/control" (coordinator: L. Garcia); and "Methodology for the evaluation of the economical cost of Echinococcosis" (coordinator: G. Battelli). Two new networks are activated at the beginning of 1997: "Long-term evaluation of chemotherapy in cystic echinococcosis" (coordinators: T. Todorov, A. Teggi), and "Natural history of small single hydatid cysts" (coordinator: Z. Pawlowski). People interested in participating in these networks or wanting to create a network, can send their name, the description of their research team, and the part they plan to take in the proposed network. All the proposals are submitted to the Coordinating Board and to Dr Meslin (WHO "Research on and promotion of zoonotic disease surveillance and control" team). If the work undertaken by a network leads to a proposal for international classification/standardization, it is submitted for formal approval by WHO. It must be understood by everyone, however, that neither WHO nor the Informal Working Group can give any financial support for these networks; however they can help in advising participants about other sources of funding, and organizing meetings on given subjects. In conclusion, the WHO Informal Working Group on Echinococcosis will continue to play a major role in information exchange and in stimulating public interest in the field. It does not exclude any active group or scientist but tries to integrate them on the basis previously defined. The coordinator designated for the 1995-1999 period is Prof. Dominique A. Vuitton, WHO Collaborating Center for Prevention and Control of Human Echinococcosis, University Hospital, F-25030 Besançon, France (Tel. xx33 3 81665572, Fax xx33 3 81665570).