Background - This paper reports dielectric dispersion occurring in potentised homeopathic medicines subjected to variable frequency electric field using an instrumentation method developed by the authors. Oscillations occur in the direction of electric field, and are usually termed longitudinal/acoustic-mode vibrations.Methods - The test material was lactose soaked with homeopathic medicine. Multiple resonance frequencies, forming a frequency-set, were observed repeatedly for each medicine.Results - We report experimental results for three potencies of Cuprum metallicum (Cuprum met) in the frequency range of 100 kHz–1 MHz. Each exhibits a set of resonance frequencies, which may be termed as its characteristic set. As the frequency-set of each medicine is different from those of others, each medicine may, therefore, be identified by its characteristic frequency-set. This suggests that potentised homeopathic medicines, which are chemically identical with the vehicle, differ from one another in the arrangement of vehicle molecules.