A cyclic voltammetric study of the oxidation of glucose on an electrochemically formed platinum oxide layer of a platinum electrode was carried out in both the absence and presence of an underpotential-deposited thallium or lead layer. An enhanced effect on the oxidation of glucose was observed in oxide-covered platinum electrodes compared to bare platinum electrodes. This enhancement remained in the presence of an underpotential-deposited thallium or lead layer. The presence of the underpotential-deposited metal layer significantly increased the anodic peak current and the response to changes in glucose concentration over the concentration range of 0 to 10800 mg/100 cm3 (0 to 0.6 M). The presence of the underpotential-deposited thallium layer appears to alter the mechanisms of the electrochemical oxidation of glucose on the platinum electrode. This is reflected by the results-the anodic peak current is directly proportional to the voltage scan rate applied in the cyclic voltammetric study on a bare platinum electrode, whereas it is directly proportional to the square root of the voltage scan rate in the presence of an underpotential-deposited thallium layer.