The small‐signal gain of cw CO2and/or N2O mixing gasdynamic lasers has been measured by varying the cavity losses with the aid of two rotating coupled NaCl plates placed within the cavity and looking for the generation cutoff point. The saturation parameter has been determined on the basis of measured values of respective small‐signal gains by experimentally recovering the output power‐cavity losses relation. The measurements yielded &agr;0≃1.1 m−1andIs≃3.2 kW/cm2for CO2, and &agr;0≃1.0 m−1andIs≃3.0 kW/cm2for a cw N2O mixing gasdynamic laser.