Strain‐amplitude–dependent internal friction was measured in pure aluminum under forced vibrations at a frequency of 8.3×10−3Hz. Using a modification of the torsional pendulum apparatus, the effects of time, cold work by bending, and changes in bias stress were investigated at room temperature. The dislocation damping theory by Granato and Lu¨cke adequately describes the results. The frequency range in which this theory has been successfully applied is thus extended several orders of magnitude below the frequencies employed to date in experiments of this kind. Similar work at much higher frequencies by other investigators compares well with the present results.