The behaviour of hydrogen, in its contact with the iridium and the tungsten filament kept at different temperatures, was studied in the pressure range 1.3 . 10-6 - 1.3 . 10-3 Pa, in a glass apparatus. The effects of adsorption, atomization, desorption, recombination of atoms and chemical reactions were investigated as a function of temperature of the filaments. The named individual processes were used for interpretation of the partial pressure changes in the apparatus. The significance of the above individual phenomena in the UHV experiments is pointed out in this paper.