Tritium instrumentation is required for the protection of personnel in any facility handling significant quantities of tritium. In such facilities, in a chronic or accidental tritium release situation, tritium may be present in the air as tritiated hydrogen gas (HT, DT, T2) or tritiated water vapour (HTO, T2O, DTO). For health protection purposes, the airborne tritium concentration of each species should be determined separately since the two species represent very different radiological hazards. This paper describes a tritium monitor that is capable of measuring the airborne concentration of tritium species in the range from 0.037 MBq/m3 (1 µCi/m3) to 7.4×104 MBq/m3 (2.0×106 µCi/m3) with a resolution of 0.074 MBq/m3 (2 µCi/m3) in the lowest range. The measurement principle is based on the separation of tritium species by a permeable membrane and the measurement of sample air activities by conventional ion chamber based tritium monitors.