Here, we found that lactic acidosis induced mitochondrial biogenesis in tumor cell lines (A-549, A-427, MCF-7), as evidenced by an increase in both mitochondrial mass and mtDNA, accompanied by high transcript levels for NRF-1, NRF-2, and TFAM in A-549 and MCF-7 cells or upregulation of these transcripts by lactic acidosis in A-427 cells. This evidence concerns the gene NRF1 and lactic acidosis.