In 1952, two American agricultural scientists visited the National Agronomic Station (EAN) in Lisbon, Portugal. Frederick Wellman and William Cowgill were at the onset of a travel across the world, which aimed to prevent the spread of Hemileia vastatrix to the American continent. In the 19th century, this fungus had almost totally destroyed Arabica coffee plantations in Africa, Asia and Oceania. Branquinho de Oliveira, head of the plant pathology department of EAN, was invited to act as a partner. He became responsible for the accommodation of coffee plants and rusts collected by the two Americans during the worldwide travel, and the material gave place to a new research line. Gradually, the idea of a new institution, to assist all coffee research centers in the world and located in Portuguese soil, emerged. An agreement was eventually signed between both governments and funds of the Foreign Operations Administration were used to create the Coffee Rust Research Centre (CIFC) in 1955, near Lisbon. Environmental conditions were the alleged reason as to why Portugal, a warm and sunny country, was considered an ideal place to centralize physiologic and breeding experiments with a tropical plant such as coffee. Is this enough to explain, however, why the United States would pick such a strange bed-fellow? Was Portuguese imperialism, under fire from the international community, a hidden part of the equation? Firmly rooted in the CIFC’ s correspondence, which has remained intact and untouched until today, the present investigation follows the trans-imperial (or transnational) circulation of seeds, plant clones and fungus enlisted to participate on a fight against what was considered to be the most dangerous threat to coffee production. This paper is not about the impact of a plague or new cultivar. It’s a story about an idea of a plague and how diplomatic, political and even epistemological wedges, separating the ‘free world’ from authoritarian and colonialist Europe, were bracketed, under the sign of ‘scientific cooperation’.