A general equation involving the reduction of trimethylamine oxide byAchromobacteris derived and tested, and is AH2 + (CH3)3NO → A + (CH3)3N + H2O, where AH2is the hydrogen donator and A the oxidized substrate. The reduction of trimethylamine oxide as hydrogen acceptor with the evolution of trimethylamine is a linear function of time in the presence of cell suspensions and single hydrogen donators including glucose, glycogen, lactate, and pyruvate. All strains ofAchromobacterare not able to reduce the oxide, although they may contain the same dehydrogenases as revealed by employing the methylene blue technique. Small concentrations of hydrogen acceptors such as nitrate and methylene blue inhibit the reduction of the oxide. Since fumarate is not inhibitive and supports anaerobic growth there is evidence of a preferential activation of hydrogen acceptors.