This paper is an outline of a wide program that is currently under development in the large territory of Argentina. The Director of the Program is Dr. Fernando Pagés Larraya; it is supported by the National Council of Scientific Researches (CONICET) and the National Board of Mental Health. The general purpose of the program is to study the prevalence of mental disorders in different ethnographic areas within the country. Epidemiology allows the forecasting of disease occurence. A research work this area may be qualified "effective" if it provides useful data for prevention programs. Therefore, it is necessary that researches and professional responsibles of Mental Health Governmental decissions work together. This rapprochment is being attempted in developing the Argentine research program. It has a cross-cultural approach. It can be called "a way of thinking" as opposed to a precise methodology. A considerable variety of research tools are being used, depending on the specific purposes and the characteristics of the ethnographic areas. One of the main difficulties in choosing a technique for "case-finding" is uncertainty about where to place the "cut-off point" between presence and absence of illness. In this program the Present State Examination (PSE) is used in population surveys of large urban centers. It is a semi-structured interview that has been extensively tested. In small rural communities, the work is done using "key-informants" and applying the snow-ball sample technique. One specific purpose of the research is the study of the modal personality structure in each ethnographic area, formulated in terms of the Holtzman Inkblot Test. The paper shows the relationships between purposes, research tools and responsible professionals. There is hardly time or surplus intellectual energy for polemic and alienation between clinicians and social scientists. Theories, methodologies, research data and prevention programs have not developed harmoniously. We need to carry out research work not divorced from Public Health responsible authorities, in order to avoid that useful data from Epidemiological Studies will not be used in prevention programs.