Gamma interferon (IFN-γ)-activated macrophages control Trypanosoma cruzi infection via nitric oxide (NO), recently recognized as a major effector molecule. Granulocyte macrophage-colony stimulating factor (GM-CSF) is a multipotent cytokine secreted by macrophages and many other cells. It induces the production of tumour necrosis factor alpha (TNF-α), another cytokine also secreted by macrophages and involved in the control of T. cruzi infection. However, no data are available on the relationship between GM-CSF, TNF-a and NO produced by macrophages activated by IFN-γ and infected with T. cruzi. To highlight this relationship, mouse peritoneal macrophages (MPM) and two c-myc retrovirus-induced macrophage cell lines (9.1.1 and BMM8), respectively characterized by a constitutive and an inducible production of GM-CSF, were activated with I FN–γ and/or GM-CSF and infected with T. cruzi. Our results indicate that T. cruzi upregulates GM-CSF release from MPM and from the two macrophage cell lines, activated (or not) by IFN-γ. A high autocrine production of GM-CSF or an exogenous supply of GM-CSF is correlated with an enhanced release of TNF-α and NO, inducing an improved control of T. cruzi infection by IFN-γ-activated MPM.