Abstract: Biofilm on glass beads deposited within a bottom portion of a vertically elongated bioreactor housing for possible experimental evaluation through a testing port in the housing which is also provided with inlet ports for aeration and infeed of nutrients with liquid. The biofilm collected within the housing chamber undergoes growth on glass slides within a cross-sectionally rectangular portion of the bioreactor housing from which the slides may be upwardly withdrawn under selective control without biofilm damage. The bioreactor housing arrangement also provides a high length to width ratio designed to enhance aeration.