A general model for the design of fluidized bed reactors operating with immobilized enzymes in spherical porous particles is presented. It was solved for monosubstrate reactions following reversible Michaelis-Menten kinetics, as well as competitive inhibition by the product. The general model also allows the evaluation of irreversible and/or non-inhibited kinetics. To check the model, experimental conversions obtained in a fluidized bed reactor were compared to those predicted theoretically. The chemical process used for the validation of the model was the hydrolysis of o-nitrophenyl-beta,o-galactopyranoside catalyzed by beta-galactosidase covalently immobilized in Chromosorb-W. The model was tested in 160 different experimental conditions.