The properties and analytical applications of a new polymetallic species containing four [Ru(bipy)(2)Cl](+) (bipy = 2,2’-bipyridine) groups coordinated to the pyridine residues of the meso-tetra(pyridyl)porphynate cobalt(III) complex are reported. The cyclic voltammograms of the tetraruthenated cobalt porphyrin, in DMF solution, exhibit an intense reversible wave at E(1/2) = 0.93 V associated with the Ru-III/II redox couple, and two irreversible cathodic waves at E(pc) = - 1.37 and - 1.63 V, involving the stepwise reduction of the bipyridine ligands in each peripheral ruthenium complex. Three successive reductions of the cobalt porphyrin center can be detected in the -0.5 to -0.7 V range, using spectroelectrochemical techniques. Stable, homogeneous films of the polymetallic porphyrin can be generated by dip-coating on to electrode surfaces, exhibiting pronounced electrochemical activity. The modified electrodes have been successfully employed for analytical purposes, using conventional and flow injection methods, showing excellent performance in the determination of reducing analytes, such as nitrite and sulphite ions, even at ppb levels.