The variations in the characteristics of several 500 V corona-stabilizer tubes have been studied in detail experimentally. Variations of striking voltage and running voltage from tube to tube have been recorded and the effects of ambient-temperature changes and of excess current on tube characteristics have been noted. The results of this work are presented together with some information on the running-voltage drifts to be expected during the first 1200 hours of life. The properties of tubes run with reversed polarity are also discussed.