Type II NADH dehydrogenases (NDH-2) are monomeric enzymes that cat-alyse quinone reduction and allow electrons to enter the respiratory chain in different organisms including higher plant mitochondria, bacteria and yeasts. In this study, anAgrobacterium tumefaciensgene encoding a puta-tive alternative NADH dehydrogenase (AtuNDH-2) was isolated and expressed in Escherichia coli as a (His)6-tagged protein.