A platinum disc microelectrode was employed to measure the diffusion coefficient of cetyltrimethylammonium bromide, CTABr, aggregates in aqueous solution and in the presence of additives: KBr, n-decanol, and KBr + n-decanol. Other micellar parameters such as the hydrodynamic radii and aggregation numbers were calculated from the micellar diffusion coefficients. The data obtained were rationalized in terms of electrolyte-induced aggregate size increase and sphere-to-rod morphology change. In the presence of solubilized n-decanol, this transition occurred at a lower KBr concentration, confirming that the micelle surface charge density, hence its dimension, is strongly influenced by adsorption of the fatty alcohol. (C) 2007 Elsevier B.V. All rights reserved.