The results obtained on highly purified titanium (5 N) have shown that the internal friction spectra after cold working (P 2) could be decomposed into two peaks, due respectively to a thermally activated depinning of dislocations pinned by hydrogen atoms and to a dragging by the dislocations of hydrogen atoms situated in their vicinity. Thus the shape of the damping spectra is modified by the hydrogen concentration. Commercially pure titanium is degassed in high vacuum at elevated temperatures and the evolution of the damping spectra obtained after cold working with respect to the time of the previous annealing confirms the hypothesis concerning the mechanisms and demonstrates the possible use of internal friction as a mean of hydrogen concentration measurement.