In helper T (Th) cells, cell fate is primarily determined by the transcription factors GATA-3, which directs Th2-type cells, and T-bet, which regulates Th1 lineage choice. Hwang et al. found that during the early stages of a T helper precursor's decision to become a Th1 cell, T-bet has an unusual means of repressing the Th2-promoting effects of GATA-3. After T cell stimulation and under the right polarizing conditions for Th1 cells, T-bet becomes phosphorylated by the tyrosine kinase, ITK, which allows it to bind GATA-3 . This process prevents it from interacting with its Th2 cytokine target genes. This study reveals a further means by which transcription factors may directly cross-regulate one another in specifying cell lineage fate.