The first observation of electrochemiluminescence (ecl) based on the redox-cycling of a ruthenium chelate covalently linked to a protein and placed in aqueous medium containing neither solvent nor reducing compound is reported here. Ecl experiments based on redox-cycling were performed in phosphate buffer at carbon interdigitated microelectrode arrays. The light intensity represented 31% of that obtained using a non complexed Ru(bpy)(3)(2+) solution prepared in phosphate buffer containing proteins.