Abstract: Acetylcholinesterase and/or a receptor of acetylcholinesterase is immobilized on a solid support and stabilized by covering with a protective film of gelatin and/or albumin containing trehalose. The film is applied by covering the immobilized acetylcholinesterase and/or receptor of acetylcholinesterase with a layer of a gel-forming solution of gelatin or albumin in an evaporable solvent containing dissolved trehalose, and evaporating the solvent to leave the film. The film provides stability against dry heat, organic solvents, proteases and changes in pH. Other additives such as polyhydric alcohols, organic solvents, polymers and/or ionic and non-ionic components may be present to increase stabilization. A diagnostic kit or chromatography column may be formed containing the stabilized immobilized acetylcholinesterase and/or receptor of acetylcholinesterase.