1) The epidemiology of Chagas’ disease was studied for the first time in a systematized work, in a district of the region of the Amazon estuary, whose ecological conditions differ from those encountered in other zones where similar researches have been made. 2) At the place chosen for the studies – Aurá – a locality about 10 kms from Belem (State of Pará), no human infection by S. cruzi has been found, either by blood examination or xenodiagnosis, both having been tried on all the inhabitants (117 people); nor was there any symptomatology attributable to the disease. 3) Out of the six xenodiagnoses made on domestic animals (five dogs and one cat), only one dog was found infected. This animal belonged to the house where the greatest infestation by triatomid bugs with a high index of infection was verified. However, for the reasons given in the text, the hypothesis that the dog might have become infected by eating organs of infected wild animals has been suggested. 4) Of the 115 animals whose blood was examined in thick blood film, 9 (7,8%) proved to be infected by Schizotrypanum. Out of 47 xenodiagnoses carried out on wild animals, 15 (32.6%) showed positive results (11 opossums, 3 ant-eaters, 1 armadillo). The ant-eater T. tetradactylus is a new vertebrate-host of Schizotrupanum. 5) During 11 months of research, each house being inspected at least once every fortnight, triatomid bugs were found in 7 out of the 36 houses of the village. The 39 specimens collected were all adults; an exhaustive search did not reveal the existence of any young insects in the houses. According to their order of frequency, the species found were the following: P. geniculatus (29 specimens, 7 infected), R. pictipes (9 specimens, 2 infected) and E. mucronatus (1 uninfected specimen). The great majority of the insects was captured during the second half of the year (summer period). 6) In the very midst of the forest, in the hole of an ant-eater (T. tetradactylus), larvae, nymphs and adults of P. geniculatus were found. The house nearest to the hole presented the highest index of infestation by this bug (22 specimens, all in adult stage). In the hole of Potus flavus (“macaco da noite”) a triatomid larva and an adult Panstrongylus rufotuberculatus have been found. 7) Strains of Schizotrypanum isolated from wild animals showed a weak virulence. The dog strain, although easily infecting laboratory animals, differs from the typical human strains, as DIAS and FREITAS proved in their biometrical studies. 8) The results above mentioned are discussed in the paper and, in view of the habits of the insect vectors and the prevalence of infected wild animals, the sylvan nature of Chagas’s disease in Aurá is concluded. Although human cases have not been detected, the possibility of human infection in this region is admitted, since a domestic animal (a dog) was found to be infected (possibly through the way of the insect vector). Attention is drawn to the confirmation such results seem bring CARLOS CHAGAS” hypothesis, that this disease was at first found in wild animals, and could later on spread to domestic animals and man.