Tin (IV) oxide was used as a bulk mediator in carbon paste and carbon ink screen-printed electrodes to improve the better performance of the carbon electrodes for the detection of hydrogen peroxide in comparison with unmodified electrodes. A new glucose biosensor developed from modified carbon paste electrode and coated with glucose oxidase entrapped in Nafion was investigated with a flow injection system. The biosensor could be operated under physiological conditions (pH 7.5, 0.1 M phosphate buffer), with an operating potential of ?200 mV (vs. Ag/AgCl), a flow rate of the carrier of 0.2 mL/min. and an injection volume of 100 μL. The amperometric response of the biosensor showed good linearity up to 200 mg/L with a detection limit (3σ) of 6.8 mg/L. The relative standard deviation for the repeatability of measurements for 100 mg/L glucose was 2.9% (n = 10 measurements) and the corresponding reproducibility was 12% (n = 5 sensors). The effect of all investigated interferences (uric acid, paracetamol, xanthine, hypoxanthine and ascorbic acid) was not fatal and could be eliminated by the use of the standard addition method. The new biosensor was successfully applied to the determination of glucose in human blood plasma.