Hypoxia stimulates a number of pathways critical to cancer cell survival, including the activation of vascular endothelial growth factor (VEGF) transcription. In normal fibroblasts, hypoxia-induced activation of the protein tyrosine kinase, Src, is required for VEGF expression. We show here in both pancreatic and prostate carcinoma cell lines cobalt chloride (used to mimic hypoxia)-induced VEGF expression requires Src activation and leads to increased steady-state levels of HIF-1α and increased phosphorylation of signal and transducer of transcription 3 (STAT3). STAT3 and hypoxia-inducible factor (HIF)-1α bind simultaneously to the VEGF promoter, where they form a molecular complex with the transcription coactivators CBP/p300 and Ref-1/APE. Expression of activated Src from an inducible promoter is sufficient to increase VEGF expression and form these STAT3/HIF-1α-containing promoter complexes. Inhibition of DNA binding by expression of either STAT3 or HIF-1α dominant negative mutants significantly reduces VEGF expression. These data suggest that the binding of both STAT3 and HIF-1α to the VEGF promoter is required for maximum transcription of VEGF mRNA following hypoxia.