Hypoxia-induced delayed neuronal death is known to requirede novo gene expression; however, the molecular mediators that are involved remain undefined. The transcription factor hypoxia-inducible factor-1α (HIF-1α), in addition to promoting the expression of adaptive genes under conditions of hypoxia, has been implicated as being a necessary component in p53-mediated cell death in tumors. Using herpes amplicon-mediated gene transfer in cortical neuronal cultures, we demonstrate that delivery of a dominant-negative form of HIF-1α (HIFdn), capable of disrupting hypoxia-dependent transcription, reduces delayed neuronal death that follows hypoxic stress. In contrast, hypoxia-resistant p53-null primary cultures are not protected by HIFdn expression. These data indicate that, in hypoxic neurons, HIF-1α and p53 conspire to promote a pathological sequence resulting in cell death.