The influence of the MoO 4 2-ions on the Bray-Liebhafsky (BL) oscillatory reaction is described. The MoO 4 2-ions affect the values of the parameters of the BL reaction; first of all, they decrease the induction period and the duration of oscillations, but they increase the average frequency of oscillations. A qualitative explanation of this influence is based on the Treindl-Noyes skeleton mechanism of the BL oscillatory reaction. The production of singlet oxygen ( 1 O 2 ) by the disproportionation of hydrogen peroxide catalyzed by molybdate ions, which is obviously quenched physically and/or chemically, may play a role too.