In the 1920s oligarchic rule in Brazil was perceived to be constantly under threat from ‘revolution’. Domestic developments and the impact of the First World War had brought about major changes in the political arena. In this context, the resources of the Ministry of Foreign Relations (Itamaraty) were systematically used by the Brazilian government as a means to monitor and counteract presumed overseas connections of a ‘revolutionary’ nature. Actions against tenentismo in the Río de la Plata region and diplomatic efforts to oppose the 1930 Revolution, among other issues, are examined in this article in order to provide further understanding of the role played by Brazilian diplomacy in the final years of the Old Republic.