The cytoplasmic membranes of many aerobic and facultative bacteria contain enzymes that catalyze the reduction of dissolved oxygen to water. Preparations of small particles derived from such membranes can be filter sterilized without loss of the oxygen-reducing enzymes. These particle preparations can be used to produce anaerobic conditions in a variety of biological environments. They have been shown to stimulate the growth of many anaerobic bacteria and can also be used to stabilize oxygen-sensitive chemical reagents. The particle preparations are stable for long periods of time. They are functional over a pH range and temperature range frequently encountered in biological systems. Various techniques for using the particles are presented. The advantages and limitations of this new approach to achieving oxygen-free conditions are discussed.