A proportional counter for the measurement of low Tritium activities is described. The cylindrical proportional counter with a volume of about 600 cm/ sup 3/ is the inner part of a low level counting system in which the guard counter (anti-coincidence counter) surrounds the principal counter (proportional counter) which is only separated from the annular counter by a thin foil. The ratio of the transmit'' to the out'' counting rate is high compared to other low level counting systems (of the order of 300). The specific feature of the design is the separation of the volume of the internal counter and the anti- coincidence counting ring. The special properties of the counter and some of its operations are discussed. (auth)