Amid rapid social changes in Brazil in the 1950s, wide-reaching collective research projects in the social sciences were conducted in partnership between Brazilian and international agencies working in regional development. Cooperation between social scientists and government staff was based on the expectation that social and anthropological studies would orient the changes then under way. By approaching the research program in the São Francisco River Valley, the article examines a turning point in the career of sociologist Donald Pierson, combining analyses of context and content in his intellectual production. Pierson concentrated initially on the institutionalization of the social sciences in Brazil, promoting a standard of sociological work based on scientific research. In his research in the São Francisco River Valley, Pierson adopted a new approach by combining the sociologists role as scientist with that of agent of social change, thereby highlighting the importance of the application of sociological knowledge in practice.