The GUERREIRO and MACHADO complement fixation tect performed in the pericardial fluid of 278 chronic chagasic patients was positive in 77,3% of those who died without cardiac failure and in 79,4% in those with light zigns of cardiac failure; those who died with pronounced cardiac failure showed only 58,4% of positivity. There was statistical difference between this last group and the others, but not between the two first.