From a viewpoint of provision of useful and reliable field monitoring data for test exercises of environmental tritium transfer models, a pine tree is examined on its suitability as a bio-indicator for monitoring. Since the current model test exercises focus on the uptake, formation and translocation of organically bound tritium (OBT) in food crops, our monitoring program was designed to obtain useful information on the OBT formation in different parts of the pine tree by uptake of tritium through the atmosphere and soil. Monitoring was conducted in ordinal environment as well as in the vicinity of tritium discharge sources. The observations allow the discussion of the dependencies of OBT formation in the foliage part or wood part of the pine tree on an air-foliage pathway. As conclusions the usefulness of OBT data of a pine tree used as a bio-indicator for monitoring is presented.