Hypoxia-inducible factor (HIF) has been recognized primarily for its role in the maintenance of oxygen and energy homoeostasis. HIF-1 and HIF-2 are heterodimeric transcription factors composed of HIF-1 and HIF-2 , respectively, which dimerize with a constitutively expressed � subunit and subsequently bind to hypoxia response elements in the promoters of target genes. The activity of HIF is regulated by a variety of stimuli, including changes in cellular oxygen concentration, growth factors and oncogenic activation. Signosis has developed HIF filter assay. Unlike conventional gel shift assays, HIF filter assay is a high throughput assay and it can analyze DNA binding activities of HIF in multiple samples simultaneously. Meanwhile, the assay can be set up for a few samples with less tedious than non-radioactive gel shift assay or much safer than 32P based gel shift assay.