The optimization task was performed using the gluconic acid synthesis by the Acefobucter methonolicrrs MB 58 strain. The microorganisms were grown continuously on methanol as the growth substrate. After finishing the growth process by the deficiency of N and P, the gluconic acid synthesis was started by adding glucose. The synthesis process was performed continuously. The oxygen transfer rate depended on the gluconic acid concentration. During the growth process, the oxygen transfer rate reached a value of about 13 g 0,. kg-I . h -I using a 30-1 glass fermenter equipped with a 6 blade stirrer and fully baffled. This rate declined to a value of between 2 and 5 g 0, . kg-I . h -' in the presence of gluconic acid concentrations above 150 g gluconic acid . kg-' medium. The yield (g gluconic acid . g-glucose) depended on the gluconic acid concentration and amounted to y = 0.7 in relation to 150 g gluconic acid . kg-I medium and y = 0.8 in relation to 200 g . kg-medium, respectively.The fermenters were coupled with ultrafiltration moduls (Fa. ROMICON and Fa. SARTORIUS). The biomass concentrations amounted from 5 to 40 g dry mass kg-' medium. The ultrafiltration modules retained the biomass within the fermentation system. A glucose solution (30 t o 50 weight percent glucose) was continuously dosed into the fermenter. The retention time was chosen between 2 and 30 h. The gluconic acid synthesis rate reached values of up to 32 g gluconic acid. kg-I . h-'. Within a range of up to 250 g gluconic acid . kg-' medium, the acid concentration had no influence on the enzyme activity.