Aims: To compare cellulase production by Aspergillus niger ATCC 10864 biofilms on polyester cloth and freely suspended cultures in shaken flasks and microbioreactors of bubble column type. Methods and Results: Both shaken flasks and oxygenated microbioreactors containing 40 ml of production medium were used to compare cellulase secretion by free mycelium and biofilm cultures. Free mycelium cultures grew better in flasks than in microbioreactors producing compact and fluffy pellets, respectively, while the opposite was found for biofilm cultures without any visible change in biofilm morphology. Cellulase activities and volumetric productivities attained by biofilms in flask cultures were 70% higher than that produced by free mycelium cultures and threefold higher when biofilms were grown in microbioreactors. Conclusions: Fungal biofilms developed on polyester cloth in both flasks and microbioreactors produce higher cellulase yields and volumetric productivities than free mycelium cultures at lower biomass levels. Significance and Impact of the Study: The results of the present study are of commercial and biological interest. All productivity parameters revealed that fungal biofilms may be used for the production of cellulase and other proteins in various types of bioreactors. Moreover, they may be used as model systems to study differential gene expression related to cell adhesion. © 2006 The Authors.