Monocytes represent a heterogeneous populationof primary immune effector cells. In humans, at least three different subsetscan be distinguished: classical monocytes (CD14++CD16-), intermediate monocytes(CD14++CD16+), and non-classical monocytes (CD14+CD16++). There is pooragreement on functional properties of the three subsets of monocytes. Takinginto account that different human inflammatory diseases evidence monocytesubsets perturbation, the aim of the present work was to characterize thefrequency and the properties of different monocyte subpopulations in blood samplesfrom seropositive patients with Chagas disease. Chagasic patients showedincreased frequency of IL-1β and nitric oxide (NO)-producing monocytes (p<0.05).However, seropositive and seronegative individuals presented similar frequencyof reactive oxygen species (ROS)-producing monocytes. Furthermore, monocytes fromseropositive patients seemed to have greater ability to hydrolyze thepro-inflammatory ATP, since they exhibited higher CD39 and CD73 expression thanmonocytes from seronegative individuals. The in vitro infection of peripheral blood from healthy donors did not modifythe expression of CD39 in the monocyte population, but significantly diminishedCD73 expression in this cell population (p<0.05). Similar to bacterial andviral infections, the proportions of classical monocytes decreased (p<0.0001),while the frequency of non-classical subset increased (p<0.01) in chronic chagasicpatients. Strikingly, non-classical monocytes presented increased NO and ROSproduction and less IL-10 production than classical monocytes. The decreasedproduction of IL-10 could be correlated with lower expression of CD39 in non-classicalmonocytes. Moreover, CD73 expression were higher in non-classical monocytes.Our data suggest that monocytes from chagasic patients exhibited augmentedinflammatory properties. Hence, it is not unusual that they might playimportant roles in promoting inflammation in human diseases.