The partial molar volume, .hivin.V, and the partial sp. vol., .hivin.n, were estd. for more than 25 polyelectrolyte structures. The materials investigated by d. measurements in highly dild. aq. solns. (c < 10-2 monomol/L) included both synthetic polyelectrolytes and chem. modified natural polymers. Through a detailed anal., related to the chem. structure and macromol. parameters, a linear dependence between the copolymer compn. and the partial vols. could be identified for diallyldimethylammonium chloride/acrylamide copolymers. Additivity could also be shown for sodium cellulose sulfate having various degrees of substitution. For a homologous series of poly(vinylbenzyltrialkylammonium chloride)s, a linear correlation between the molar mass of the monomer unit and the partial molar volume was obtained. No influence of the d.p. was obsd. as long as the contour length exceeds the Debye length. The exptl. results were used to evaluate the general applicability of the additivity schemes of Durchschlag and Zipper, as well as Gianni and Lepori, to polyelectrolytes. Agreement between exptl. and calcd. partial vols. strongly depends on the chem. structures. In the case of the synthetic polycations, the deviations are in a similar range for both models though somewhat smaller for the Gianni/Lepori model. The use of the Durchschlag/Zipper model yields much better agreement for the anionic biopolymers with deviations generally less than 3%. The tendency of the empirical models is correct; however, the precision may be improved by regressing of parameters from the exptl. results. The new exptl. data may also be useful in polyelectrolyte characterization. [on SciFinder (R)]