The cytochrome c oxidase (COX) family of proteins function as the final electron donor in the respiratory chain to drive a proton gradient across the inner mitochondrial membrane, ultimately resulting in the production of water and ATP. The mammalian COX apoenzyme is a dimer, with each monomer consisting of 13 subunits, some of which are mitochondrial and some of which are nuclear. COX7b (cytochrome c oxidase subunit VIIb polypeptide) and COX7b2 (cytochrome c oxidase subunit VIIb polypeptide 2) are 80 and 81 amino acid proteins, respectively, which exist as components of the COX complex, therefore playing an important role in electron transport. A rare polymorphism in the COX7b2 gene at codon 26 may be linked to nasopharyngeal carcinoma (NPC), the most common head and neck cancer in southern China.