A highly active tetramethylphenylenediamine-oxidase has been found in association with the cell wall blebs, evaginations of the outer wall membrane, of Neisseria meningitidis. Isolated wall blebs consumed oxygen in the presence of ascorbate-tetramethylphenylenediamine but not in the presence of succinate, whereas cell envelope preparations are active on both substrates. The ratio of succinate dehydrogenase/tetramethylphenylenediamine-oxidase activities in preparations of envelopes was approximately 100 times that in isolated wall blebs, indicating that the outer membrane preparations were highly purified.