The decrease of the quenching agent found in aged counters (approximately 2×108counts registered) is of the order of 0.5%. This cannot account for their bad functioning. Only changes on the anode surface (polymer deposit) and in the gas phase (new products formed by counter discharge) are responsible for the deterioration of aged self‐quenching G‐M counters. The first mentioned changes are neutralized by simply glowing the wire, the latter may be overcome by the choice of a suitable quenching agent. C2H5CN gives better results than C2H5OH.