Abstract: A method is described for testing the serviceability of a seismic torsional vibration damper. In the method, a test piece, which is constructed as a viscosity torsional vibration damper and whose seismic mass is enclosed entirely liquid-tight, is flanged to the free end of a torsion-spring bar, which, in its turn, is bolted in a torsionally stiff manner onto a large stationary mass. The test piece is excited to a free, decaying natural vibration by a rotational impulse. The damping factor of the decaying response vibration is determined separately for each period by routine measurement of the amplitudes of vibration. For "healthy" test pieces, the sequence of the damping factors determined must fall in value and lie inside a predetermined falling scatter band. Should the characteristic of the damping factor be of a different type, this indicates that the viscous damping medium has aged more or less strongly and provides a measure of the serviceability of the test piece.