Abstract: Nonsymbiotic hemoglobins are broadly present across evolution; however, the function of these proteins is unknown. Cultured maize cells have been transformed to constitutively express a barley hemoglobin gene in either the sense (HB+) or antisense (HB?) orientation. Hemoglobin protein in the transformed cell lines was correspondingly higher or lower than in wild type cells under normal atmospheric conditions. Limiting oxygen availability, by placing the cells in a nitrogen atmosphere for 12 hours, had little effect on the energy status of cells constitutively expressing hemoglobin, but had a pronounced effect on both wild type and HB? cells, where ATP levels declined by 27% and 61% respectively. Energy charge was relatively unaffected by the treatment in HB+ and wild type cells, but was reduced from 0.91 to 0.73 in HB? cells suggesting that the latter were incapable of maintaining their energy status under the low oxygen regime. Similar results were observed with P.