The examination by complement fixation test (Machado-Guerreiro) of 379 blood samples randomly assembled in 6 localities of the county of Jaguarão (Rio Grande do Sul - Brazil), showed only 10 positive cases (2,64%). Norte of the positive people is native to Jaguarão; ali are immigrants from nearby endemic areas. Owing to the Umited number of positive people it is not possible to correlate serological prevaience for Chagas'Disease and eletrocardiographic abnormalities. These abnormalities showed a high prevaience rate apparently related to sustained blood tension among some of the examined people. In conclusion: 1) Chagas'Disease is not endemic in the county of Jaguarão; 2) The high rate of eletrocardiographic abnormalities is related to the prevalence of altered blood tension.