Adenosine is an endogenous metabolite produced during hypoxia or inflammation. Previously implicated as an anti-inflammatory mediator in CD4(+) T cell regulation, we report that adenosine acts via dendritic cell (DC) A(2B) adenosine receptor (A(2B)AR) to promote the development of Th17 cells. Mouse naive CD4(+) T cells cocultured with DCs in the presence of adenosine or the stable adenosine mimetic 5'-(N-ethylcarboximado) adenosine resulted in the differentiation of IL-17- and IL-22-secreting cells and elevation of mRNA that encode signature Th17-associated molecules, such as IL-23R and RORγt. The observed response was similar when DCs were generated from bone marrow or isolated from small intestine lamina propria. Experiments using adenosine receptor antagonists and cells from A(2B)AR(-/-) or A(2A)AR(-/-)/A(2B)AR(-/-) mice indicated that the DC A(2B)AR promoted the effect. IL-6, stimulated in a cAMP-independent manner, is an important mediator in this pathway. Hence, in addition to previously noted direct effects of adenosine receptors on regulatory T cell development and function, these data indicated that adenosine also acts indirectly to modulate CD4(+) T cell differentiation and suggested a mechanism for putative proinflammatory effects of A(2B)AR.