Horseradish peroxidase (HRP) immobilized on TiO2 coated cellulose microfibers was used to study the catalytic oxidation of pyrogallol to purpurogallin in a flow injection (FI) system. The Michaelis-Menten constants for the enzymatic oxidation were determined for the immobilized enzyme, K-m=47 mM and V=22 mu mol min(-1), and compared with those obtained for free enzyme, K-m=11 mM and V=53 mu mol min(-1). The activity of the immobilized enzyme is reduced presumably due to its interaction with the oxide surface. However, the level of activity of the immobilized phase does not decrease with time under the conditions used in the FI system after various operation cycles.641763309315