Sliding spark array, corona and Ge semiconductor preionisers were compared in a small TEA CO2 laser by looking at their effect on the output energy of the laser. The corona and semiconductor preionisers provided good pulse-to-pulse repeatability (˜5%) with a clear discharge whilst the spark array was less repeatable (˜12%) and caused a dark deposit to appear on the electrodes. The semiconductor system was the least efficient and the sliding spark the most efficient system, with the corona providing a good compromise between the two. Of the three types tested, the corona preioniser was prefered overall. © 1987.