Levels of genetic variation and population structure were determined for 181 Triatoma sordida insects from four populations of southeastern Brazil, through the analysis of 28 allozyme loci. None of these loci presented fixed differences between any pair of populations, and only two revealed polymorphism, accounting for low levels of heterozygosity (H(e) = 0.027), and low genetic distances (D < 0.03) among populations. F(ST) and Contingency Table results indicated the existence of genetic structure among populations (F(ST) = 0.214), which were incompatible with the isolation by distance model (Mantel test: r = 0.774; P = 0.249).