A Vibrational Unconfined Compression Tester has been developed which superimposes applied vibration upon axial compression for a cylindrical sample of cohesive material. The VUCT has been applied to systems of wet sands. During applied vibration, the material retreated into elastic space within each vibration cycle. The top cap stress/axial strain curve progressed through a series of hysteresis loops. The instantaneous values of peak axial stress, P-i, and averaged values, P-ave, have been compared with peak stresses for control tests with no applied vibration, P-nv. P-ave always gave lower values than P-i, due to the cyclic nature of the system. However, in some tests P-i was not significantly different from P-nv. Thus, P-ave is not an appropriate parameter for determination of the effects of vibration upon material strength. In some cases, vibration caused a genuine reduction in material strength as measured by peak stress. This depended upon applied vibration and material properties. The maximum reduction in strength did not correspond to resonance frequency.