In a greenhouse experiment, some features of Tritium migration from an aqueous feeding solution to white willow (Salix alba L.) habitat components and isotopic effects of hydrogen during the willow growth have been studied. A number of rate constants for tritiated water diffusion through pores, cell membranes and uptake through the root system (k = (8.44±0.03)•10-7 s-1); 3 H/ 1 H isotopic exchange in OH-groups of organic substances (k = 5.07•10-7); "isotopic lightening" during photosynthesis (k = 5.00•10-8) were calculated from the experimental data. The rate constant of tritium transfer through the root system to intercellular sap of plants is 2.17±1.45•10-6 s-1. The tritium distribution between the feeding solution and the intercellular sap has come to equilibrium within 1-2 weeks. The fractionation factor (α) is 0.88-0.94 and does not depend on the concentration of 3 H in the feeding solution. The rate constant of transformation of tritium into organically bound species is 8.6±3.0•10-7 s-1. The equilibrium has set from 4 to 11 weeks, α = 0.17-0.19 and does not depend on 3 H concentration in the feeding solution. At the same time, strong isotopic effect of "lightening" of the feeding solution, probably owing to transpiration, has been observed. The rate constant value of Tritium transpiration calculated from the experimental data is 2.67±0.27•10-8 s-1. The rate of tritium removal due to transpiration is proportional to its concentration in the feeding solution. The factor of tritium fractionation during transpiration is 1.35±0.08.