A family of transcriptional activators has recently been identified in chickens; these transcriptional activators recognize a common consensus motif (WGATAR) through a conserved C4 zinc finger DNA-binding domain. One of the members of this multigene family, cGATA-3, is most abundantly expressed in the T-lymphocyte cell lineage. Analysis of human and murine GATA-3 factors shows a striking degree of amino acid sequence identity and similar patterns of tissue specificity of expression in these three organisms. The murine and human factors are abundantly expressed in a variety of human and murine T-cell lines and can activate transcription through a tissue-specific GATA-binding site identified within the human T-cell receptor δ gene enhancer. We infer that the murine and human GATA-3 proteins play a central and highly conserved role in vertebrate T-cell-specific transcriptional regulation.