The reaction of hydrogen (or deuterium) and oxygen on pure polycrystalline platinum surfaces has been investigated in the 10-5 to 10 -6 Torr range using the matrix isolation and laser-induced fluorescence techniques. Water, formed with a 1.1±0.2 kcal/mole activation energy, was the only product detected by infrared spectroscopy at catalyst temperatures between 150 and 700°C. Laser-induced fluorescence experiments were used to observe the production of HO radicals both in argon matrices and in the gas phase. HO production was found to have an activation energy of 31±1 kcal/mole and could only be detected escaping from the surface at catalyst temperatures above 500°C. The dependence of H 2O and HO radical production on the partial pressures of H 2 and O2 has been made. Reaction mechanisms are discussed in relation to other studies of the oxidation of hydrogen on single crystal and polycrystalline platinum surfaces.