The compact, universal plate mixer is sufficiently small to be used in any lab situation and mixes solutions by means of a continuous small orbital motion which is 4.5-mm in diameter. The high speed and small diameter of orbit in this plate shaker combine to offer a true vortexing action in each well of the microplate. This action ensures both complete and uniform mixing. For situations in which more than one microplate needs to be mixed simultaneously, a dedicated double microplate holder accessory can be readily bought. Additional accessories may also be purchased for use with the microplate mixer which allow the shaking of up to 48 sample tubes.