The critical study of the papers published up to 1951 on Chagas' disease in the State of Minas Geraes (Brazil), was divided into five chapters: 1) Work made in Lassance; 2) Work made in Bambuí; 3) Work made in Belo Horizonte; 4) Work made in other parts of the State; 5) Large-scale prophylaxis of Chagas' disease. 1) The work made in Lassance covers a long period of almost 30 years, from 1909, when a new trypanosoma was discovered and the corresponding disease was described by Chagas, up to 1936. The researches made in Lassance were carried out by Chagas and its co-workers of the Oswaldo Cruz Institute. During this period they described the various clinical features of the new disease, made a detailed study of its agent and the biology of the transmitting insects, and experiments and studies on the pathogeny and pathology of the disease; they developed diagnostic methods, analysed the role of domiciliary and wild reservoirs, and insistently showed the social significance of this sanitary problem. 2) The research work made on Chagas' disease in Bambuí contributed decisively for the growing interest on the study of this disease during the last few years. Although the work in Bambuí was carried out continuously since its beginning in 1940, the researches may be divided into two groups, namely the preliminary made before the installation in the mentioned city of the Center for the Study and Prophylaxis of Chagas' Disease in November 1943, and the work done after the installation of the Center. The first group represents the first contribution after the researches carried out in Lassance, towards a formal study of acute cases of Chagas' disease in the State .The finding of numerous acute cases at Bambuí led the direction of the Oswaldo Cruz Institute to create a Center of Studies in that city. An outstanding contribution on the clinical, epidemiological and prophylactic fields was brought about by investigators of Manguinhos with the abundant material supplied by the Bambuí Center. The chief contributions from Bambuí were of three kinds: a) The individualization of the chronic Chagas' heart disease on clinical, anatomo-pathological, electrocardiographic and experimental basis; the demonstration of its great frequency in infected individuals and the verification that in certain rural areas schizotrypanosis is one of the most important etiological factors of heart disease. b) The experience acquired with the use of the complement fixation reaction with antigens of cultures of Schizotripanum cruzi allowing a rapid and safe confirmation of chronic cases of schizotrypanosis. The reaction, if done in a large-scale, make it possible to get a fairly accurate idea on the incidence of Chagas' disease in endemic areas. c) The possibility of performing prophylactic campaigns by using proper residually acting insecticides. 3) — An examination of the literature on the subject shows a delayed interest of scientifc investigators and clinicians of Belo Horizonte on the study of Chagas' disease, since the first papers are dated 1930...