The hormone erythropoietin (EPO), which is synthesized in the kidney or liver of adult mammals, controls erythrocyte production and is regulated by the stress-responsive transcription factor hypoxia-inducible factor-2 (HIF-2). We previously reported that the lysine acetyltransferase CREB-binding protein (CBP) is required for HIF-2α acetylation and efficient HIF-2–dependent EPO induction during hypoxia. We now show that these processes require acetate-dependent acetyl CoA synthetase 2 (ACSS2). In human Hep3B hepatoma cells and in EPO-generating organs of hypoxic or acutely anemic mice, acetate levels rise and ACSS2 is required for HIF-2α acetylation, CBP–HIF-2α complex formation, CBP–HIF-2α recruitment to the EPO enhancer and efficient induction of EPO gene expression. In acutely anemic mice, acetate supplementation augments stress erythropoiesis in an ACSS2-dependent manner. Moreover, in acquired and inherited chronic anemia mouse models, acetate supplementation increases EPO expression and the resting hematocrit. Thus, a mammalian stress-responsive acetate switch controls HIF-2 signaling and EPO induction during pathophysiological states marked by tissue hypoxia.