A xylose-oxidizing membrane-bound aldose dehydrogenase was purified from Gluconobacter oxydans subsp suboxydans ATCC 621. The enzyme did not require added coenzyme for activity and could oxidize d-glucose, d-xylose, d-galactose, d-mannose and l-arabinose. d-Glucose was oxidized 1.6 times faster than d-xylose. The enzyme had a molecular mass of 87 kDa and appeared as a single polypeptide. Nitrotetrazolium blue — phenazine methosulphate and dichlorophenol indophenol — phenazine methosulphate were efficient electron acceptors.