Abstract: The present invention concerns a gas analyzer, for instance a CO.sub.2 analyzer, comprising a measuring chamber for the gas to be examined, a reference chamber from which the gas to be measured has been drawn off, a light source and a chopper disk, which chops the light beam to make it pass alternatingly through the measuring and reference chambers and so that in between there is a period during which no light is passed through at all, and an automatic gain control which maintains a constant difference between the "dark" signal and the signal delivered by the reference chamber. An attenuation member is positioned adjacent the reference chamber so the light beam passing through the reference chamber is attenuated to cause a shift of the operating point of the gain control circuit into the gently ascending part of the absorption versus concentration curve.