Adaptation to hypoxia represents an important aspect of tumor progression. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates essential homeostatic responses to cellular and systemic hypoxia by activating transcription of multiple genes including those encoding glycolytic enzymes and vascular endothelial growth factor (VEGF). In this report, we demonstrate that whereas C-SRC expression is not required for expression of HIF-1 or transcriptional activation of genes encoding VEGF and enolase 1 (ENO1), cells expressing the v-Src oncogene have increased expression of HIF-1, VEGF, and ENO1 under both hypoxic and nonhypoxic conditions. Expression of V-SRC was associated with increased transcription of reporter genes containing cis-acting hypoxia-response elements from the VEGF and ENO1 genes, and this transcriptional activation required an intact HIF-1 binding site. When three rat hepatoma subclones that differed with respect to the level of HIF-1 expression were injected into nude mice, tumor growth correlated with HIF-1 expression, suggesting that HIF-1 may be generally involved in tumor progression. These studies link an oncogene to the induction of HIF-1 expression, thus providing a mechanism for hypoxic adaptation by tumor cells.