Triatoma sordida, a predominantly peridomestic species, is currently the triatomine species most frequently collected in Brazil. To evaluate the effectiveness of control activities against this species, a survey to determine infestation rates was carried out in October 1993 in 12 rural localities in the municipality of Porteirinha, State of Minas Gerais, Brazil. In the survey, 772 T. sordida were captured, of which 3.6% were infected with Trypanosoma cruzi. Of the 406 dwellings investigated, 34.9% were infested, and 27.6% of 695 peridomiciliar ecotopes contained T. sordida. The area around the dwellings was relatively uniform, with few positive ecotopes per household and low triatomine densities (a maximum of five insects per colony). The study found an association between the presence of insects and wood: 72.8% of the insects were captured in this type of ecotope. The majority of the positive households (62.9%) were close to forests (12 to 299 m); 92.3% of the infested ecotopes were less than 20 m from the house. A census of peridomestic animals revealed that chickens were the most abundant (82.7%). All positive households found in the survey were sprayed immediately with deltamethrin (25 mg a.i./m2). New surveys were carried out 7 months (survey 2) and 12 months (survey 3) after spraying. In survey 2, the number of insects collected corresponded to 52.5% of the original total, and in survey 3, 79.1%. The decrease in population observed in survey 2 was mainly due to a reduction in the population of nymphs. The large proportion of adults captured in that survey supports the idea that T. sordida produces only a single generation per year in this region. In survey 3 the increase in the number of nymphs, attributable to the great availability of chickens as a source of food, resulted in population growth. Despite the difficulties of spraying and the short persistence of the insecticide, the slow population response of T. sordida suggests that one annual spraying is sufficient for effective control of this species. Higher effectiveness could be obtained by eliminating peridomestic hiding places, for example, by replacing wooden annexes with structures made from other materials.