The dynamic behaviour of agarose aggregates grown in binary mixtures of water and dimethyl sulphoxide (DMSO) has been investigated by Transient Electric Birefringence (TEB). Different agarose concentrations in various water/DMSO compositions have been studied. The birefringence relaxation has been fitted by means of a stretched exponential with an exponent of 0.5 which suggests highly size-polydispersed aggregates. The rotational diffusion coefficient, [D-rot], has been seen to depend strongly upon the composition of the binary solvent and to increase markedly with increasing electric field. The gradient d[D-rot]/dE has been thus considered a relevant parameter. For low agarose concentrations d[D-rot]/dE displays a maximum for a solvent composition in the vicinity of f(DMSO) = 0.17 (mole fraction). Also, d[D-rot]/dE varies as a power of concentration whose exponent first increases with increasing DMSO proportion and then levels off at nearly the same mole fraction (i.e. f(DMSO) = 0.17) The results are discussed in the light of the occurrence of a ternary complex (agarose/water/DMSO), a model of organization within the agarose fibres recently proposed from thermodynamics investigations.