This article examines the relationship between the Rockefeller Foundation (RF) and Brazil in the era of Dr. Carlos Chagas, from the RF’s first visit to Brazil in 1916 to the late 1920s. Chagas’s discovery in 1909 of a hitherto unknown human disease (American trypanosomiasis) made him arguably the best-known medical scientist in the country. As the federal director of public health and the director as well of the Oswaldo Cruz Institute, he appeared to be well positioned to collaborate fruitfully with RF initiatives in public health and medical education. Yet in many respects the relationship was not what was hoped for. Using RF and Brazilian sources, the article examines the political, medical, and other divisions in Brazil that complicated and to a certain extent frustrated Brazil’s relationship with the RF; only in the 1930s, under different political circumstances, did the relationship flourish. The article emphasizes the national dimensions in the success or otherwise of the RF’s agenda in international health.