A house sprayed 104 days before with BHC was selected for demolition. It was sited in the municipality of Russas, an endemic area of Triatoma braziliensis, in the farm of Boa Vista. Bug capture in the area revealed that of 171 T. braziliensis 48.8% were infected with Trypanosoma cruzi. Only five Triatoma pseudo maculata were caught. Of the 250 inhabitants of this farm 7.7% had positive serology for T. cruzi infection (indirect immunofluorescent test). 9.1% of dogs had positive xenodiagnoses. In the house to be demolished one inhabitant had positive serology but 26 T. braziliensis captured before dmolition were all uninfected. During demolition an rat infected with T. cruzi was found and of 104 triatomine bugs 89.4% were T. pseudomaculata and 10.6% T. braziliensis. Infected Rhodnius nasutus was found in the chicken house. Examples of T. pseudomaculata were found in the roof (0.6 per swquare metrejand in the external an internal walls of the living room (0.8 per square metre). Precipitin tests of blood meals revealed marked anthrophilia. We believe this house to have been initially colonised by T. braziliensis. After sprying this species was substituted by T. pseudomaculata a species feeding on man with a infection rate sufficient to effect transmission.