This paper attempts to show how leading contemporary disciplines influenced the discovery of Chagas' disease and the formation of the early disease concept. Chagas was among the first generation of Brazilian trained scientists who incorporated modern principles of tropical medicine in its research. Thus, Chagas was familiar with characteristics of vector borne tropical diseases such as malaria and yellow fever. The detection of a hitherto unknown trypanosome in the gut of a reduviid bug prompted him to search for a related (...) vector borne disease. Among the disciplines that were influential on Chagas' discovery and early disease description were pathology, entomology and parasitology. Parasitology as a new discipline was of crucial importance to tropical medicine and had a political dimension in the context of colonial medicine. Hence, leading scientists in tropical medicine were located in European countries and in the United States of America. One of these was the German Schaudinn School of Protozoology. The early description of American Trypanosomiasis can also be seen as a reflection of the Schaudinn School of Protozoology which dominated Chagas' scientific orientation towards parasitology with regard to the interpretation of the observed phenomena of the life cycle and the morphology and biology of T. cruzi. The first Chagas' disease concept was based on research of the biology and entomology of the trypanosome and its vector as well as on pathological studies of fatal cases. This concept was characterized by a confusion of some of the chronic forms of the disease, as iodine deficiency and goitre were endemic in some rural regions in Brazil. Therefore, early concepts of the disease faced strong opposition and even raised doubts about its existence. (shrink)