Virus diseases continue to represent serious health problems in most parts of the world. In spite of the fact that diseases such as polio- myelitis and measles have been controlled in the industrialized countries by vaccination, vaccines now in use in tropical countries have proved not to be optimal. Further research is needed to develop new vaccines that will be effective in all countries. To do so we need to understand better the immune response to different viruses so that we may be able to maxi- mize the protective response of new vaccines and minimize their potential immunopathologic effect. An exciting new discovery which is now being further developed is the possibility of being able to use some viruses (e.g. vaccinia, adenoviruses, etc.), as carriers for other antigens. This may open up the way for the production of vaccines that will be inexpensive and that will confer long- lasting immunity after only one injection. This meeting has also served to review our present knowledge of virus diseases which are still of great importance such as hepatitis, dengue and influenza.