A seroepidemiological study on Chagas disease was undertaken in 281 individuals with age ranging from 3 to 75 years in the rural locality of Caballito, Simon Planas Municipality, Lara State, Venezuela (9º 45´´ LN - 69º 15´´ LW). One hundred and thirty one were males (46,6%) and 150 females (53,4%). Blood samples were obtained from each of the patients by venous puncture and serum was separated. The presence of specific circulating antibodies was quantitatively determined by indirect fluorescence antibody test, using as antigens epimastigotes of a local strain of Trypanosoma cruzi and, as a control, promastigotes of Leishmania braziliensis to detect cross reactions. As a conjugate was used anti human IgG labeled with fluoresceine. The reaction was considered as positive with titers 1: 8 or over. Sixty-eight (24,2%) had circulating antibody to T. cruzi and 34 (12%) to L. braziliensis. Most of the positive results were found in persons over 20 years old, but the highest results were found in the group from six to ten years. The Strout technique was negative in all of the cases. One hundred and six specimens of Rhodnius prolixus were captured, 46 adults and 60 nymphs, out of which 32 (30,2%) were positive to T. cruzi. All of the positive persons live in huts all made with wall of earth, 5 (9,4%) besides, had dry palm leaves roofs and 46 (86,8%) roofs were made with zinc laminas. 50 (94,3 %) of the surveyed inhabitants state to know the vector that they call popularly «chipo»