A technique of immobilizing very thin layer of enzymes over glass electrodes, resulting in response times as low as 5-10s, is described. The method involves the adsorption of enzyme molecules onto the sensitive end of the glass electrode followed by the formation of covalent bonds between the enzyme molecules, by means of spraying a dilute solution of glutaraldehyde over the surface. Enzymes immobilized in this manner over pH glass elctrodes are acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), penicillinase, and urease. The cross-sectional scanning electron micrograph of the fractured surface of the electrode shows the immobilized layer is not more than 1-2 µm thick. The technique could offer immense scope for immobilization of other protein substances as thin layers on different support surfaces.