We present pulse height measurements for 5-keV Auger electrons from a radioactive Fe-55 source mounted at the inner cathode surface of cylindrical proportional counter, which is operated with CH4 admixed dry air or N-2. A clear shift of the pulse height has been observed by varying the amount of the admixtures; the number of electrons, created in the primary ionization by Auger electrons, is decreased by the electron attachment of the admixtures during their drift from the place near the source to the anode wire. The large gas amplification (typically 10(4)) in the secondary ionization of proportional counter makes it possible to investigate a small change in the number of primary electrons. The electron attenuation cross-section of O-2 has been evaluated by analyzing the shifts of the pulse height caused by the electron attachment to dry air and N-2. (C) 2013 Elsevier B.V. All rights reserved.