Experimental tests performed in vacuo indicated that a chemical adsorption reaction can be used to facilitate the cryopumping of H with liquidN-cooled condensers. Cryopumping is accomplished by reacting H with O to form H2O, which will readily condense on a liquid-N-cooled surface. The reaction in vacuo was performed on a solid catalyst, which consisted of a bed of Pd-coated alumina pellets. Cryopumping was observed at pressures as low as about 0.4 micron of mercury. A laboratory cryopump consisting of 5.8 lb of catalyst and a liquid-N-cooled condenser achieved a pumping speed of about 570 l/sec at 1.0 micron of Hg. A laboratory model of a cryopump which could be used in an electric rocket test facility was studied. The experimental data obtained were used to estimate the size of the catalyst bed necessary to test a 50-kw electric thermal rocket with an H propellant flow rate of 0.00063 kg/sec (a pumping speed of 580,000 l/sec at an operating pressure of 10 microns of Hg. (Author).