The S. cerevisiae flavohemoglobin (YHB) shares extensive homology with the bacterial globins in Vitreoscilla, Escherichia coli, and Bacillus subtilis, suggesting an ancient origin and a possible common function for members of this protein family. However, unlike its bacterial counterparts, YHB is induced during logarithmic growth and in oxygen-replete conditions. YHB transcription is aerobically regulated by the heme-responsive transcription factors HAP1 and HAP2-5, while anaerobically there is low-level HAP-independent gene expression. Surprisingly, no glucose repression of YHB transcription is evident, which is novel among the HAP2-regulated heme proteins studied. A hap1 strain also shows no glucose repression of YHB, suggesting a HAP2-regulated activity that is insensitive to glucose-repression. A hap2 strain displays increased YHB transcription in glucose, indicating that the HAP1-regulated activity is best in this carbon source. Immunolocalization of YHB place it as a soluble, cytoplasmic protein. These studies argue against an hypothesized role for the flavohemoglobin assisting in mitochondrial respiration and instead suggest a separate and as yet unknown function for YHB in S. cerevisiae aerobic metabolism.