Thymic stromal lymphopoietin (TSLP) is a cytokine that promotes CD4+ T cell homeostasis and contributes to allergic and inflammatory responses. TSLP can act directly on mouse CD4+ T cells, but in humans, the available data have indicated that TSLP receptors are not expressed on CD4+ T cells and that TSLP instead activates dendritic cells, which in turn promote the proliferation and differentiation of CD4+ T cells. We now unexpectedly demonstrate the presence of TSLP receptors on activated human CD4+ T cells. Strikingly, whereas freshly isolated peripheral blood human T cells show little if any response to TSLP, TCR stimulation allows a potent response to this cytokine. Moreover, TSLP increases the sensitivity of human CD4+ T cells to low doses of IL-2, augmenting responsiveness of these cells to TCR engagement. Our results establish that human CD4+ T cells are direct targets for TSLP.