The authors report on their experience with the nitrofuranes among 37 patients with acute Chagas' disease treated according to schemes of long acting action. All patients had a direct positive parasitologic test for Chagas'disease. The therapeutic response was based, mairily, on the xenodiagnostic and the Guerreiro-Maehado test, which were taken as often as possible or whenever it was felt neoessary, no matter what the result of the parasitologic test could be. The results showed that the nitrofuranes, espedally the nitrofurazone and the nitrofurfurylldene derivative "Bayer" 2502, are active agents against the T. cruzi, as seen through the manifest diminuitíon of blood parasites - by means of the xenodiagnostic test, the Guerreiro-Machado test which becomes negative, and also through the shortening of the clinical manifestations. A close relationship between the results of the xenodiagnostic test and the Guerreiro-Machaçlo test after treatment could be noted. In most patients a supressive response could be observed, while in eight patients there was an apparent curative effect. They emphasize the need to evuluate the therapeutic results during treatment, the necessity of keeping the patients under observation, for the side effects are common. The authors finally conclude that the nitrofurfurylidene derivative "Bayer" 2502 shoud be given to patients with acute Chagas' disease.