Attenuated total reflectance Fourier transform infrared spectrometry has been employed to assess the degree of chlorination of hydantoin moieties which are covalently linked to the surface of the polyamide, Nylon 66. The N-chlorinated hydantoin functional groups are active in producing biocidal activity against pathogenic microorganisms upon direct contact with the surface molecules of the fabric. Chlorination of the treated Nylon 66 causes a blue shift of the hydantoin amide bands which can be conveniently monitored as a quality control procedure in the production of the biocidal fabric.