Ultrastructural in situ hybridization was used to visualize the spatial distribution of poly (A) RNA and quantitate its relative amount within different cellular compartments of cardiomyocytes after T. cruzi infection. The amount of poly (A) RNA remained about the same up to 24 h post-infection. In contrast, its content was reduced 65% after 72 h of interaction, showing a marked decrease in the cell cytoplasm. This decline in poly (A) RNA level in host cell cytoplasm was concomitant with intracellular proliferation of T. cruzi amastigotes. Thus, T. cruzi may affect host cell cytoplasmic mRNA stability, associated with the parasite's intracellular multiplication.