A mechanism that we have proposed for bovine plasma amine oxidase predicts that under anaerobic conditions (single turnover) 1 mol of benzaldehyde and 1 mol of NH4+ are produced from benzylamine. Other works have reported experiments with amine oxidases from other sources that show that NH4+ is not released under anaerobic conditions. The amount of NH4+ and benzaldehyde released when plasma amine oxidase acts on benzylamine under anaerobic conditions has been determined to resolve this discrepancy. It was found that 1 mol of NH4+ and 1 mol of benzaldehyde are released per active site. This result is consistent with the mechanism that we have proposed but is inconsistent with other mechanisms that invoke pyridoxal as an active-site component of amine oxidase.