A rapid, convenient, and fundamentally-sound flow adsorption technique for mesuring monolayer hydrogen uptakes of cobalt, iron, and nickel catalysts is described. It involves cooling the reduced catalyst in flowing hydrogen from the reduction temperature to about 190-200 K (dry ice-acetone temperature), desorbing in argon at about 200 K for about 15 min, and finally desorbing in argon while heating to the reduction temperature at about 10-25 K/min. Desorbed hydrogen is monitored by thermal conductivity. A simple flow apparatus equipped with manual control valves, a manual pressure regulator, and a thermal conductivity cell can be used to collect data. This method avoids some of the pitfalls of (i) earlier reported flow techniques in which removal of reversibly chemisorbed hydrogen occurs at 273 or 298 K and (ii) earlier reported static techniques involving long equilibration times during which hydrogen spillover onto the support causes erroneously high uptakes to be obtained. Metal crystallite diameters estimated from hydrogen uptakes obtained by this new flow procedure are in good-very good agreement with those estimated from X-ray diffraction and transmission electron microscopy for cobalt, iron and nickel catalysts.