Mutual diffusion coefficient values for binary aqueous solutions of both L-glutamic acid (H(2)Glu) and sodium L-glutamate (NaHGlu) were measured with the Taylor dispersion technique, at T = 298.15 K, and concentrations ranging from (0.001 to 0.100) mol.dm (3). The results were discussed on the basis of the Onsager-Fuoss and the Nernst theoretical equations, by considering the H(2)Glu as a weak acid (monoprotic acid, with K-2 = 5.62 . 10 (5)). The smaller values found for the acid with respect to those of the salt, confirm this association hypothesis. From the diffusion coefficient values at infinitesimal concentration, limiting ionic conductivities as well as the hydrodynamic radius of the hydrogen glutamate ion (HGlu) were derived and analyzed in terms of the chain methylene groups. The effect of different phenomena, such as association or complexation, were also taken into consideration and discussed. Values for the dissociation degree for H(2)Glu were also estimated. (C) 2014 Elsevier Ltd. All rights reserved.