5-Azacytidine treatment of T. cruzi epimastigotes in culture induces active cell proliferation. This effect was detected as an increase in the cell number and [ 3 H-methyl]thymidine incorporation into DNA. 5-Azacytidine does not alter other metabolic parameters. We have previously demonstrated that 5-azacytidine induces DNA hypomethylation in T. cruzi. Accordingly, we suggest that this chemical modification may be related to the control of T. cruzi cell division.