An optical fibre probe based on glucose dehydrogenase immobilized on nylon was constructed. The probe was used to quantitate glucose through a measurement of the fluorescence of the NADH formed by the enzyme-catalyzed reduction of glucose in the presence of NAD. The probe response was reproducible and displayed good linearity in the concentration range of 1.1 to 11.0 mM glucose. The limit of detection was 0.6 mM glucose. The response was affected by pH and NAD concentration.