Abstract: The present paper reports that the exchanges between iodide ions or bromide ions and cetyl iodide or cetyl bromide in n-butyl alcohol which are studied for the first time by radiotracer method follow a second-order kinetics (SN2 mechanisms). The corresponding kinetic and/or thermodynamic parameters are obtained. The rates of these exchanges are found to be as follows:I-for-I>I-for- Br>Br-for-I>Br-for-Brwhich in turn is explained in terms of solvent effects. The theoretical treatment and the experimentation reported may also be applicable to similar reactions.