A small mud hut, which was built by its owners in 1949, was known, since 1951, to be one of the houses most heavily populated by triatomid or cone-nosed bugs in Bambuí. A total of 2 505 individuals, belonging to the species Triatoma infestans, were collected there from October to December, 1951, in 26 applications of pyrethrum powders into the holes of the walls. Three years later, in December, 1954 no less than 4 645 bugs were collected the same way, in five consecutive days. The hut was destroyed in January 13, 1955 when 1 398 additional insects were collected. Then, a total of 8 548 specimens of Triatoma infestans were captured in this single house, while only 4 P. megistus were captured. It has been observed that the proportion of bugs naturally infected with S. cruzi decreased from 37,7 per cent in 1951 to 6,5 per cent in 1954. The percentage of infected adult individuals dropped from 61,5 to 9,4 and "nymphs" it dropped from 33,3 to 3,5 in respectively 1951 and 1954. These differences were found to be statistically significant. All the six people inhabiting this hut exhibited a positive complement-fixation test (S. cruzi culture antigen) and xenodiagnosis was positive in 4 of them. Haemograms taken from 5 of them showed varying degrees of anaemia. The head of the family, 49 years old, was a Chagas' disease case with right bundle-branch block, while the electrocardiogram was normal in the other people. The las-born child of the couple died at the age of 14 months with fever and oedema, so it was possibly a case of acute schizotrypanosis.