The ability to assess oxygenation within living cells is much sought after to more deeply understand normal and pathological cell biology. Hypoxia Red manufactured by Enzo Life Sciences is advertised as a novel hypoxia detector dependent on nitroreducatase activity. We sought to use Hypoxia Red in primary neuronal cultures to test cell-to-cell metabolic variability in response to hypoxic stress. Neurons treated with 90 min of hypoxia were labeled with Hypoxia Red. We observed that, even under normoxic conditions neurons expressed fluorescence robustly. Analysis of the chemical reactions and biological underpinnings of this method revealed that the high uptake and reduction of the dye is due to active nitroreductases in normoxic cells that are independent of oxygen availability.