A new mechanism is proposed for the atmospheric production of OH radicals. The mechanism involves a sequential two-photon absorption by atmospheric H2O molecules. The first photon excites H2O to a high vibrational state (H2O*), and the second promotes H2O* to a dissociative electronic state. Theoretical calculations are combined with the results of experimental measurement to assess the importance of this mechanism as a source of atmospheric OH. The collisional quenching rate of H2O* is found to be a crucial factor in the relative contribution of the proposed mechanism to OH production at different altitudes. We believe that it is likely that the quenching rate is too rapid for the two-photon mechanism to contribute significantly in the atmosphere, although the energy transfer rates for highly excited H2O* have yet to be measured in the laboratory.