Mother-to-child transmission of intracellular parasites could be related to the production of immunoregulatory cytokines. The levels of gamma interferon (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and lnterleukin (IL)-10 were evaluated during pregnancy in sera of women chronically infected with Trypanosoma cruzi that delivered infected or non-infected children. The levels of IL-10 increased in both, women only pregnant and only infected, compared to non-infected non-pregnant women. However, in pregnant women chronically infected with T. cruzi, IL-10 did not increase significantly, neither in the mothers of infected nor in the mothers of non-infected children. The levels of the inflammatory cytokine TNF-alpha were not affected in normal pregnancy but increased in the infected mothers of non-infected children. The levels of IFN-gamma did not increase in the groups studied, indicating that the production of this pro-inflammatory cytokine was controlled, even when the levels of IL-10 did not increase, as in pregnant women chronically infected with T. cruzi.