Communication: In luminescence-based oxygen sensors the active luminescent species is usually a transition metal complex immobilized in a polymeric matrix-in most cases a ruthenium(II) polypyridine complex. In an attempt to overcome some of the disadvantages of these systems, a polymer-immobilized iridium(III) complex has been prepared and used for the first time as the active species in such a sensor. The luminescence properties of this system are described and its drawbacks with regard to sensors technology discussed.