Three synthetic paths have been used to prepare iron-based catalysts for the electrochemical reduction of oxygen in solid polymer fuel cells. The catalyst precursor used in the first synthetic path was a dispersion of Fe(OH)(2) on carbon black (Vulcan) that was reduced at 600 degrees C in H-2. The second synthetic path involved a method to intercalate FeCl3 that was first used with graphite and then extended to Vulcan. The oxidized iron was reduced by either heating the resulting materials at 600 degrees C in H-2 or by reacting them at room temperature with K-naphthalene in a nonaqueous solution. In the third synthetic path, Fe particles were generated directly on Vulcan by the reduction in a nonaqueous solution of FeCl2 with triethylborohydride. All these iron containing materials were then activated at 1000 degrees C in the presence of acetonitrile in order to transform them into active catalysts for O-2 reduction. The best catalyst was obtained by extending the intercalation method of FeCl3 to carbon black (Vulcan) and then reducing the oxidized iron with K-naphthalene. Based on electrochemical and physicochemical analysis (mostly scanning electron microscopy and x-ray diffraction analysis) it is suggested that iron is included or intercalated in the carbon black particles. The higher catalytic activity of this material compared to the others is explained by the progressive release of the iron from the carbon black particles and its reaction with acetonitrile during the final thermal activation step at 1000 degrees C.