The LB 110 is a special measuring system for monitoring the tritium activity concentration in room and exhaust air. The monitor LB 110 measures the tritium activity concentration directly, largely specifically, ensuring the highest possible sensitivity obtainable with today’s state of the art. Gaseous radionuclides other than tritium or an increased background radiation level can be detected separately in a second measuring channel; thus the influence of these components on the tritium measurement due to the selected measuring method only slight, anyway can be compensated for still further. The monitor LB 110 consists of two separate units: the pump and other detector unit incorporating the operating electronics for which, depending on the intended application, different systems from the Berthold program are available. The function units have been designed as plug-in modules which are inserted from the front panel, thus, the monitor is quite easy to service.