Abstract: A catalyst is disclosed, which can be used for carrying out, in a continuous manner simultaneously and in one and the same reaction space, two or more stages of a biochemical conversion reaction which is of the kind requiring, for certain reaction stages, the presence of an enzyme, and for other reaction stages the presence of a microorganism. The catalyst comprises solid bodies of one or more polymers of which at least one is a cross-linked polymer. At least one enzyme is bound to the polymer material of the solid bodies by covalent bonds, and at least one microorganism is physically entrapped in the three-dimensional structure of the cross-linked polymer of the solid bodies.