Microbial cellulose (MC) is being investigated for various applications in the field of biomedical engineering. Gluconacetobacter xylinus is able to produce pure cellulose in the form of a hydrogel ("pellicle"). The pellicle consists of a defined tridimensional structure that is sensitive to mechanical stress during the process of formation. The bacteria, however, are obligate aerobic and need to be supplied with oxygen. These two objectives are often conflicting. A lab-scale membrane bioreactor prototype was developed which is able to efficiently produce a MC pellicle with a homogeneous layered structure. A hydrophilic microfiltration polyethersulfone membrane separates the bacteria from the cultivation medium. This setup allows the free convective exchange of the cultivation medium, while providing mechanical support for the continuous formation of the MC layer. Thickness of the MC layer was measured online by a laser triangulation sensor. One hundred and twenty five gram cellulose dry weight/m(2) membrane surface were produced within a process time of 330 h. Membrane bioreactors may be used to produce homogenous MC layers in a variety of shapes suitable for biomedical applications. Biotechnol. Bioeng. 2011; 108: 2237-2240. (C) 2011 Wiley Periodicals, Inc.