A novel pH oscillator has been constructed by combining the pH clock reaction system BrO3--SO32--H+ with Mn2+ as a proton-consuming species. The system exhibits large-amplitude pH oscillations typically between pH = 2.8 and pH = 7.3 at 45 degrees C in a continuous-flow stirred tank reactor. The oscillatory waveform is similar to that of a pulse wave, and the duration of both high-pH and low-pH stages can be changed in a wide range by controlling the input concentrations of BrO3- and Mn2+. The state diagram spanned by the input concentrations of BrO3- and Mn2+ takes the form of a cross-shaped diagram. It has been found that MnO4-, in place of Mn2+, is also effective in consuming H+ to give large-amplitude pH oscillations. A possible reaction mechanism for the removal of H+ has been discussed in which MnO(OH)(+) is reduced by HSO3-to give HS2O6-. This properly accounts for the stoichiometry for both the Mn2+ and MnO4- systems. The proposed reaction scheme is unique among pH oscillators reported so far in that the sulfite ion plays a key role in both the nonlinear production and consumption of protons.