Epidemiological investigations about American trypanosomiasis (Chagas' disease) in the area of Bairro da Ilha, County of Salto de Pirapora, S. Paulo State, Brazil, are reported. Twenty eight houses submited to the selective technique of insecticide spraying (BHC), was tested by Gómez-Núñez method. The results obtained showed that several houses still retains with infestations in a proportion not significatively different to the before the one noticed insecticide treatment. Only a reduction of the general infestation index was obtained. Beside this some evidence showed the possibility of the occurrence of natural foci of the infection. The rodents Akodon arviculoides and Oryzomys nigripes were found naturally infected by the use of xenodiagnosis technique. In the house environment, infections was found to persist, through the examination of new born or new introduced dogs and cats, little after the houses selective desinsetization. Two cats were found infected, one of them suggest to have adquired the infection by congenital way. The other positive animal, was introduced from another area. So we conclude by the necessity of a thorough revision of the prophylactic methods of Chagas' disease based only on the control of triatomids by insecticide use.
