The levels of IFN-gamma, TNF-alpha, IL-10, and TGF-beta1 cytokines associated with Trypanosoma cruzi during pregnancy were determined by enzyme-linked immunosorbent assay (ELISA) in serum samples from peripheral, placental, and cord blood of chronic infected mothers with detectable and undetectable parasitemia, and in their uninfected newborns. Compared to uninfected pregnant women and mothers with undetectable parasitemia, the concentrations of IFN-gamma were higher at the 3 sites in mothers with detectable parasitemia. In these mothers and their newborns, the TNF-alpha concentrations were higher in the periphery and cord in comparison to serum samples from non-chagasic pregnant women. TNF-alpha levels were higher in newborns of mothers with detectable parasitemia than in newborns of mothers with undetectable parasitemia. IL-10 and TGF-beta1 levels at the 3 sites were unchanged and diminished, respectively, in samples from infected mothers with patent parasitemia in comparison with uninfected pregnant women. Cytokine concentrations did not change significantly in all samples from mothers with undetectable parasitemia; however, the concentration of TGF-beta1 was significantly reduced in their peripheral samples but significantly higher in the placenta in comparison with uninfected mothers and mothers with detectable parasitemia, respectively. These results suggest that elevated numbers of circulating parasites in vivo elicit production of pro-inflammatory cytokines that control congenital T. cruzi infection.