The cytokines IL-4 and IL-5 are often coordinately produced by Th2 cells as in asthma. However, it is unclear whether similar molecular mechanisms underlie transcription of the two genes. We have previously shown that the transcription factor GATA-3 is expressed in Th2 but not Th1 cells and is crucial for activation of the IL-5 promoter by different stimuli. In a different study, GATA-3 was shown to be sufficient for the expression of IL-4 and other Th2 cytokine genes. Here, we show that ectopic expression of GATA-3 is sufficient to drive IL-5 but not IL-4 gene expression. Also, in Th2 cells, antisense GATA-3 RNA inhibits IL-5 but not IL-4 promoter activation. The induction of IL-5 gene expression by GATA-3 involves high affinity binding of GATA-3 to an inverted GATA repeat in the IL-5 promoter.