We have used the rotating disk electrode (RDE) to measure micellar long-time self-diffusion coefficients (D-s) and intermicellar interaction parameters (k(d)) for cetyltrimethylammonium chloride (CTAC) micelles as a function of KCl concentration. D-s values were found to be a function of surfactant concentration and the observed behavior conformed to the linear interaction theory up to 1.00 mol dm(-3) KCl. The electrolyte concentration dependence on D-s exhibited three regions of behavior. With increasing KCl concentration, D-s initially increased because of increasing Coulombic screening and then decreased linearly because of a linear spherical expansion of the micelles resulting from the increasing aggregation number, N-agg Finally, D-s decreased precipitously because of the micellar structural transition from spherical to rod-shaped particles and associated electrolyte-dependent micellar elongation. Intermicellar interaction parameters were also found to be a function of electrolyte concentration and exhibited two distinct regions of behavior. At high electrolyte concentration (> 1.00 mol dm(-3) KCl), k(d) reflected thestrong interaction between growing rodlike particles while, over the electrolyte concentration range 0.00-1.00 mol dm-3 KCl, interaction parameters correlated with the calculated Coulombic interparticle interaction energy.