A number of iridium porphyrins adsorbed on pyrolytic edge plane graphite electrodes have been examined for their electrocatalytic activity toward the four-electron reduction of dioxygen. Their behavior provides insight into the mechanisms by which the iridium porphyrins accomplish this electrocatalysis. Certain iridium porphyrins are found to reduce dioxygen to water via a four-electron pathway in a monometallic fashion. Axial ligation from the edge plane graphite electrode to the iridium metal center is believed to be essential for the catalytic reduction of dioxygen to occur. We propose the active species to be an Lr(lI) center. The electrocatalytic behavior of all of the iridium porphyrins which have been examined can be explained by the transformation of these porphyrins to such catalytically active Ir(II) centers.