The gas temperature has been measured at the axis of the positive column of a number of discharges commonly used for CO2lasers. The measurements have been made with an interferometer. For the first series of measurements the tube is filled initially with 2‐Torr CO2and 4‐Torr N2. Next, He is added in steps. In the second series the gas mixture also contains a small amount of H2O vapor. If the power input into the column is kept constant the gas temperature decreases when He is added.