An experimental tube to obtain accurate and reproducible data relating to the efficiency of the hollow cathode discharge had a cathode of two plane‐parallel plates with variable separation, and a movable anode to eliminate the anode fall region. The cathode temperature was kept between 25° and 35°C by employing pulse techniques. Preliminary studies performed in helium and neon at pressures between 2 and 15 Torr gave the following results: (a) The transition from the plane cathode discharge into the hollow cathode discharge is a smooth function of the cathodic plate separation. (b) For each tube current and pressure there exist two or more optimum values of the cathodic plate separation for which the tube voltage has a minimum. The optimum distances depend on type of gas, pressure, and tube current. (c) For fixed tube current, the relative maximum decrease in tube voltage with respect to the plane‐cathode discharge voltage is, in most cases, larger in helium than in neon. (d) The variations of the discharge voltage and current with pressure are consistent with the Townsend scaling law for certain values of cathodic plate separation.