Specific features of metabolism of different classes of tritium compounds have been studied in experiments with rats and mice. The results indicated the value of intracellular content of water is by 15–40% less than the average content of water in the whole tissue. Protracted retention in lungs of particles of luminous compounds and Ti tritide inhalated or introduced into trachea was shown. So, the particles are assigned to class Y according to ICRP. Foreign low-molecular organic tritium compounds are effectively excreted with urine. Biogenic tritium compounds are bound in tissues at synthesis of biopolymers in dependence on need of body in them. According to our experiments, 1 to 90 % of tritium is separated from all incorporated compounds into body water in the form of HTO. The obtained metabolic data along with results of new radiobiological experiments on mice for RBE and biogenic tritium compounds effectiveness were the basis for development and introduction in Russia of standards for insoluble and biogenic tritium compounds and separately - for labelled precursors of nucleic acids.