The Bureau of Mines is investigating the catalytic activity of rare- earth compounds to develop a catalyst for the cathode reaction of a hydrogen-oxygen fuel cell. This report presents the results of studies of the catalytic activities of lanthanide oxides for the oxidation of hydrogen at 150 deg to 250 deg c. Preliminary activity tests were made with approximately stoichiometric mixtures of hydrogen and oxygen diluted with helium. A series of tests were also run under oxygen-rich conditions in which specific rate constants and activation energies were determined. Variations in rate constants up to 2,000 times were observed for the various lanthanide oxides. The three most active catalysts were oxides of ce, pr, and eu, having specific activities of 6.93 X 10-7, 4.88 X 10- 7, and 4.06 X 10-7 moles h2 . Sec-1 . M-2, respectively, at 200 deg c.