According to the invention, the metal vapor laser tube comprises a cylindrical plasma tube (1), which is located inside a leak-proof container (2) and which is surrounded by a thermal insulating material, an electrode (6) at each end of the plasma tube, and a cylindrical return conductor (9) coaxial to the plasma tube (1) which is connected with one of the electrodes, and characterized in that the return conductor (9) has a radius R of about: ##EQU1## where: e=exponential function,r=radius of the plasma tube, expressed in centimeters,dE/dV=energy density of the plasma, expressed in millijoules per cubic centimeter,ro=specific resistance of the plasma, expressed in Ohms.times.centimeter,U=electrical field, expressed in volts per centimeter.