In the period 1957-1971 surveys for triatominae bugs were made in 889,972 dwellings among 11,045 different localities throughout the State of Bahia, Brazil. 35,588 bugs were collected and among 29,156 examined, 2,354 (8%) were infected with trypanosomes considered to be T. cruzi. However, rates of natural infection varied from 0-100% according to species and localities. The highest rates of natural infection were found among P. megistus in the northern littoral areas of the State. Overall rates of infection by species were: P. megistus, 11,4%; T. infestans, 3.4%; T. brasiliensis, 3%. T. rubrofasciata were found often infected with T. conorhini but were not considered important as carriers of T. cruzi. The Authors consider that the presence of infected domiciliated bugs in the areas investigated implies active transmission of T. cruzi, and that vector control measures should be undertaken. The active spread of T. infestans in the State of Bahia is emphasized as a matter for particular concern, in view of this species susceptibility to infection, its anthropophilic habits and its capacity to colonize rapidly and stablish high rates of infestation.