We propose a novel mechanism for OH production in the mesosphere (50--100 km): the reaction of ground state oxygen atoms with vibrationally excited H2, which is formed via collisional energy transfer from O2 (b 1&Sgr;g+). Using published rate coefficients and altitude profiles for the chemical species involved, the contribution of this new mechanism to the total OH production rate has been estimated as a function of altitude. At altitudes above 75 km, the proposed reactions are as important as the reaction of water with excited state oxygen atoms, O(1D). The fraction of total OH produced from the proposed mechanism is estimated to reach 16% at 100 km. ¿ 2001 American Geophysical Union