This Letter is concerned with the presence of H2O2H+ in the gas phase. During the studies on the identification of the principal species produced by the CH4/O-2 microwave (MW) discharge, we have succeeded in determining the presence of the protonated hydrogen peroxides H2O2H+ in the gas phase. The mass spectra of the discharge plasma, obtained by a direct sampling system, clearly show the peak m/z 35 (H2O2H+), giving the direct evidence that H2O2H+ is formed in the plasma environment and detected mass spectrometrically. The influence of certain discharge variables on yield and concentration of H2O2H+ were investigated.