The study was carried out in San Antonio Rayón, Jonotla, Puebla, México, from August 2002 to May 2003. The objetive was determite the natural infection index to Trypanosoma cruzi. The metod consist in sprinkling piretrids to 10% at ecotopes of bugs. From a total 388 specimens there were 62 females, 48 males and 278 nymphs. There were 30 triatominae bugs infected with Trypanosoma cruzi. The entomological index were: 44.65% infestation, 4.04 stacking, 1.8 density, 90.625% colonization and 18.40% natural infection. The triatominae bugs were identified as Triatoma dimidiata (Latreille, 1811). In the main were founded within houses, this suggests us that housing quality and the modification of environment with agricultural and cattle objetives may favored the invasion into human dwellings.