the technique for the fabrication of protein-immobilized organic films was studied. a thin organic film 100 nm thick was deposited on the surface of substrates by the plasma polymerization technique, then the surface of the film was treated with a glow discharge in nh//3 gas. surface characterization by x-ray photoelectron spectroscopy was performed. the results indicated that a thin organic film with amino groups on its surface was formed on the substrates. rabbit anti-human serum albumin igg was immobilized on the surface of the film. the fab'-sh domains were separated from the protein molecules and purified. the sulfydryl groups of the molecules and the amino groups on the surface of the film were cross-linked by a bifunctional reagent. using this method, binding sites of the molecules with the supporting material can be uniquely specified. the density of the immobilized protein molecule was estimated from the enzyme immunoassay measurement, and the results suggested that a high immobilization density (approximation 6 $multiplied by$ 10**1**1 cm** $minus$ **2) could be achieved by this method. (author abstract) 15 refs