Apparatus is described for the measurement of the natural longitudinal resonant frequencies of metal bar specimens. The specimen is driven by the application of an alternating electrostatic force between one end and a small fixed plate parallel to it. The resonance is detected by a frequency-modulation system, working at 60 Mc/s, using the same plate as for the drive. The specimen mounting and drive arrangements are described and details given of the frequency-modulation and detection circuits.The equipment has a considerably wider frequency range than previous designs and measurements can be made, not only of the fundamental resonant frequency, but also of the frequencies of a series of higher modes of vibration, on specimens of widely differing sizes. These observations, when corrected for small degrees of anisotropy, enable the values of the true isotropic moduli to be derived to an accuracy of one or two parts in 10³.