A large-aperture cold-cathode electron beam with 150 kV and 0.4 A/cm2has been used to sustain 1-μs discharges in a CO2-laser mixture of 3/(1/2)/1. The electron density produced in the gas was approximately cm-3and thus for 1 atm a discharge power density of 150 J/1μs was achieved at 5.4 kV/cm for the sustainer electric field. The time-dependent gain for the 001-100 transition has been measured. Taking the experimental values of the discharge power, the gain has also been calculated using a kinetics program and a solution of the Boltzmann equation for the fractional power transfer. The good agreement between the experimental and calculated results gives confidence that the performance of cold-cathode electron-beam sustained-discharge CO2lasers can be predicted.