Two different strains of acetic acid bacteria, Acetobacter methanolicus and Acetobacter aceti, were grown on various carbon sources and their quinoprotein alcohol dehydrogenase (ADH) activities were measured. A. aceti was able to grow only on glycerol or glucose as a sole carbon source. The addition of another carbon source to a glycerol-containing medium promoted growth and increased the level of ADH activity. The results indicate that while ADH was constitutively produced under the growth conditions, an inactive form of ADH was formed besides the active form in cells grown in the medium containing glucose, acetic acid, or succinic acid. A. methanolicus was able to grow on a variety of carbon sources. ADH was formed in cells grown on glycerol or ethanol but not on methanol. ADH was also produced in cells grown on glucose or succinic acid, but the major part seemed to be the inactive form. The inactive form of ADH was thus shown to be produced under various growth conditions in both strains.