Chagas' disease is endemo-enzootic in periurban and rural sections of the first seven (18 degrees 30'-34 degrees 36' South lat.), out of the thirteen political-administrative regions of Chile. Permanent inhabited localities situated at different altitudes over the sea level (OSL) are classified in: coastal settlement (0-1,499 m OSL), intermediate settlement (1,500-3,000 m OSL) and altiplano settlement (> 3,000 m OSL). A total of 1,558 dwellings and their occupants from regions I and II were surveyed in 1982-1984 for different epidemiological Trypanosoma cruzi infection parameters. Hence, 261 dwellings, 189 domestic mammals and 517 people (ages 5- > or = 60 years) from the Altiplano settlement were studied. The results obtained were: 4(1.5%) and 2(0.8%) of dwellings infested with Triatoma infestans, according to occupants information and by observation of direct evidences respectively; 8(4.2%) animals (1 dog, 4 goats and 3 sheep) with a positive hemagglutination test (IHAT) for Chagas' disease; 21 people (4.1%) with a positive IHAT; 4(19.0%) and 3(14.3%), out of the 21 IHAT positive individuals with all types of electrocardiogram (EKG) abnormalities and EKG abnormalities suggestive of a chagasic etiology respectively, whereas 65(13.1%) and 15(3.0%), out of the 496 IHAT negative ones presented the same kinds of EKG abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)