Using a transgenic approach, we studied the role of GATA-3 in T cells. As previously shown, enforced GATA-3 expression in transgenic mice inhibits Th1 differentiation of CD4 T cells, but unexpectedly, both type 1 (interferon gamma) and type 2 (interleukin (IL)-4 and IL-13) cytokine genes were activated in the transgenic CD8 T cells. Because IL-13 gene expression was highly enhanced in vivo by GATA-3 expression, we studied the human and the mouse IL-13 gene promoters and found an evolutionary-conserved association of a consensus GATA binding site and two GATG motifs. We showed that efficient GATA-3 binding to this regulatory sequence required these three motifs and that the affinity of the GATA zinc fingers for this association was five times higher than for the consensus GATA binding site alone. Transfections in a T cell line or transactivation by GATA-3 showed that the combination of the three sites was required for full transcriptional activity of the IL-13 gene promoter. Finally we showed that this association of binding sites causes a very high sensitivity of the IL-13 gene promoter to small variations in the level of GATA-3 protein. Altogether, these results indicate an important role of GATA-3 in CD8 cytokine gene expression and demonstrate that a critical network of GATA binding sites highly modulates GATA-3 activity.