AbstractAs part of a program to investigate the use of biological nitrogen fixation for fertilizer ammonia production, an investigation into the immobilization of the aerobic, nitrogen‐fixing bacterium, Azotobacter vinelandii was undertaken. Immobilization was accomplished by adsorption onto an anionic exchange cellulose (Cellex E)with loadings as high as 1011cells/g resin. Immobilized cell preparations were tested under both batch and continuous‐flow conditions. Nitrogenase activity as high as 4200 nmol/min g resin were observed as measured by the acetylene reduction assay. Immobilized cells retained their activity for as long as 177 hr in a continuous‐flow reactor. Activity loss appeared to be related to the development of a variant strain.