The cytokine MIF is over-expressed in tumors and is associated with tumor proliferation, angiogenesis and metastasis. Hypoxia, a hallmark feature of tumors, increases MIF expression from tumor cells. We examined the role of hypoxia-inducible transcription factors on MIF secretion from MCF-7 breast carcinoma cells. Secretion of MIF was induced by hypoxia after 24h but up-regulation of MIF mRNA was minimal. Inhibition of HIF-1alpha, HIF-2alpha, NF-kappaB and C/EBPbeta using siRNA had no effect on hypoxia-induced MIF secretion. However, inhibition of transcription and translation significantly decreased MIF production, suggesting that hypoxia-induced secretion of MIF in MCF-7 cells is via an alternative pathway.