An amperometric enzyme gas-diffusion electrode has been developed which combines a porous, air breathing gas-diffusion electrode with an enzyme [glucose oxidase (GOD)] immobilized with Nation into its porous catalytic layer. The catalytic layer contains pyrolyzed Co- tetramethoxyphenylporphyrine (CoTMPP), which is very active towards the electrochemical oxidation of H2O2. The behavior of this electrode was investigated when the oxygen needed for the enzymatic reaction was supplied from the air (in the gas phase) through the porous structure of the gas-diffusion electrode. It was shown that in the presence of the substrate (glucose), the amperometric signal obtained in this mode of operation was much higher than that obtained when only the oxygen dissolved in the electrolyte was involved in the enzymatic reaction. The developed enzyme gas-diffusion electrode allows a versatile and rapid change in the O2 concentration in the zone where the enzymatic reaction is taking place. This electrode can be used as a model system for the investigation of the influence of O2 on the performance of both the peroxide or the mediated enzyme electrodes in an effort to develop oxygen independent biosensors.