The production of hydroxyl radical following either the reaction of H2/O2 mixtures or the dissociation of H2O on polycrystalline nickel has been studied in a flow system. The hydroxyl radicals were detected in the gas phase by laser-induced fluorescence (LIF) following desorption from the catalyst surface at temperatures above 850 K. The apparent activation energy for OH desorption from nickel varied from 26 to 40 kcal/mol depending upon the O/H ratio. The effect of the partial pressure of O2 and H2 on the OH production rate was measured and a mechanism to explain these results is proposed. The reaction of CO + H2 over polycrystalline nickel was also studied. However, no OH radicals were detected desorbing from the surface at temperatures up to 1350 K.