the object of this investigation is the determination of the activity of enzymes, for instance, glucose oxidase (gox), immobilized on chalcogenide and silver halide fiber surfaces. after different ways of chemical modification of the fiber surfaces, two different silanes, 3-aminopropyltriethoxysilane (3-apts) and gamma -glycidoxypropyltriethoxysilane (gpts), are used under different conditions as an enzyme carrier. the so-treated ir fiber materials are tested with colorimetric enzymatic assays using a modified flow reactor, a static method and finally an in situ cuvette measurement technique. the colorimetric detection principle is based on the oxidation of a chromogen, either the 2,2'-azino-bis-3-ethybenzthiazoline-6-sulfonic acid (abts) or the 3,5-dichloro-2-hydroxy-benzenesulfonic acid (dchbs), and aminoantipyrine (aap) system catalyzed by peroxidase (pod). the method of analyzing, testing and comparing the chemically modified fiber described, is found to be very convenient for the development and optimization of ir fibers used for ir chemical sensors. the investigated techniques show a simple, sensitive and rapid way to determine the activity of the sensors based on small pieces (3 to 10 cm) on fibers chemically modified under different conditions