A strain of Bacillus amyloliquefaciens was cultivated in a membrane recycle bioreactor for the production of an extracellular alpha-amylase. Continuous cultivations of B. amyloliquefaciens in the recycle fermenter led to higher cell mass and volumetric productivities than the ones obtained in batch or chemostat cultivations; the alpha-amylase activities were lower than in the batch mode but significantly higher than in the chemostat mode. The operation of the membrane recycle bioreactor was sometimes disturbed by high broth viscosity leading to a stronger fouling of the membrane.