A potent DPNH oxidase and a DPN-linked lactic dehydrogenase was demonstrated in Neisseria. Most organisms contained less of these enzymes than the N. gonorrhoeae isolates. An acetate oxidizing enzyme system was present in large quantities in Escherichia coli and Staphylococcus aureus, in small quantities in N. sicca and N. catarrhalis and in traces in a few isolates of N. gonorrhoeae. The system was absent from N. meningitidis. The Thunberg technic with tetrazolium salt as the electron acceptor was employed. All Neisseria contained a cyanide-sensitive aerobic cysteine oxidase and a cysteine desulf-hydrase.