The bonding of enzymes to self-assembled monolayers (SAMs) of alkanethiols onto gold electrode surfaces is exploited to produce an enzyme biosensor. The attachment of glucose oxidase to a SAM of 3-mercaptopropionic acid was achieved using carbodiimide coupling. The resultant biosensor showed good sensitivity to glucose and a large dynamic range when measured amperometrically via the p-benzoquinone mediator. On the other hand, subsequent platinization of the enzyme-SAM electrode allowed hydrogen peroxide produced in the enzyme reaction to be detected directly, thus obviating the need for an artificial redox mediator. The performance of such sensors constructed on bulk gold electrodes was evaluated and finally compared to that of some preliminary thin-film gold electrodes. Biosensors constructed using the two alternative electrode surfaces have quite different sensitivities, thus reflecting the influence of the anchoring surface on the performance of the biosensor.