Abstract: The separation of dissolved and/or undissolved materials having different densities or different buoyancy densities can be effected with the aid of agents comprising solutions of true metatungstates. In the case of a separation of materials having different buoyancy densities by means of a density gradient centrifugation, the agent has the form of an aqueous solution of an alkali, ammonium or alkaline earth metal metatungstate and, if desired, may be augmented by the addition of at least one low molecular weight electrolyte. The agent can have a density of up to 3.1 g.cm.sup.-3, has a low viscosity at high concentrations, and is neutral and chemically insert. In the case of a separation of water-insoluble solid mixtures of different densities, the densities of the solutions of the true metatungstates can be increased up to 4.6 g.cm.sup.-3 by adding to the solutions high density materials such as sodium tungstate or tungsten carbide of suitable grain size so as to form a suspension.