This paper presents an experimental examination of the behaviour of vibrationally fluidised granular materials. This work was principally focused on examining the resonant behaviour of these systems. The harmonic response of a column of various granular materials (Geldart type A and B) was measured using a small apparatus. These materials displayed several non-linear effects such as; a normalised response that was dependent on excitation level, multiple harmonic components in the response to a single excitation frequency, and odd behaviour in terms of the motion of the emulsion. Two resonant peaks were found for each material. The relative magnitudes of these two peaks were heavily dependent on excitation level, so much so that at high levels of excitation only the higher resonant frequency was present. In each case, some correlation was found between this resonant peak and a prediction based on a "granular-gas" estimate of the speed of sound in the fluidised emulsion. This correlation was farther examined by studying the resonant of the system under various levels of partial vacuum. The prediction followed the trend correctly. (c) 2006 Elsevier B.V. All rights reserved.