.Starting from an asymmetric distribution of the fatty acid/soap molecules between two chambers separated by the dialysis membrane, one chamber containing aggregates (micelles or vesicles) and the other containing buffer solution only, the rate of attainment of equilibrium was monitored. An equilibrium state was readily obtained in the case of the micellar system (micelles formed in the diffusate chamber and the fatty acid/soap concentrations in both chambers became the same). In the case of vesicles, however, the attainment of an equilibrium state was severely hindered (the concentration in the diffusate increased