The primary structure of hepatoredoxin from bovine liver mitochondria was established. It consists of 117 amino acid residues. The identity of the amino acid sequences of bovine hepatoredoxin and adrenodoxin from bovine adrenal cortex mitochondria was shown. It is assumed that the role of a ferredoxin component in mitochondrial steroid-hydroxylating systems from different organs is played by the same [2Fe-2S]-protein.