Experimental results are presented on the effect of diluent cooling of a 1721‐Å high‐pressure xenon laser produced with a pulsed beam of high‐energy electrons. Both helium and argon were used as diluents in order to limit the rise in the gas temperature that occurs when the electron beam is stopped in the gas. In the Xe&sngbnd;He mixtures the chemistry was not significantly altered by the presence of He; but in the Xe&sngbnd;Ar mixtures, argon was very important in the absorption and transfer of internal electronic energy. The results demonstrate that both diluents improve the operational characteristics of the laser. Only helium is found to improve the efficiency of conversion of electron‐beam energy into stored laser energy.