Abstract: The invention relates to biologically active protein molecules, such as enzymes, attached to water-insoluble solids to render the molecules insoluble. In one aspect the attachment is effected by molecules of diazotized m-diamino-benzene adsorbed on a surface of the solid and chemically linked to the protein molecules. This invention also provides methods for reactivating inactivated biologically active material characterized by a water-insoluble solid with a surface to which has been adsorbed molecules of a diazotized aromatic amine chemically bonded to biologically active protein molecules. One method comprises a) adsorbing additional molecules of a diazotized aromatic diamine on said surface, and b) attaching fresh biologically active protein molecules to said additional molecules of diazotized aromatic diamines.