Abstract: A composite membrane structure for immobilizing biologically active materials, such as enzymes, is formed by coating a microporous polymeric membrane with a thin layer of an inert proteinaceous material, such as zein or collagen, so that the resultant coated membrane retains intercommunicating capillary pores that extend through its structure. Immobilization of a biologically active material is carried out by contacting the coated membrane with the biologically active material in solution and drying. Biologically active materials immobilized on the membrane can be used to perform biochemical reactions and are useful in carrying out tests for glucose and uric acid.