Mutual diffusion coefficients have been measured for several average compositions of the system sodium cholate sodium deoxycholate-water at 25 degrees C. The experiments have been grouped in different sets having constant concentration of one component and variable concentration of the other one. Following this approach, it has been found that the trends of the main- and cross-term diffusion coefficients can be interpreted on the basis of the diffusion and equilibrium results of similar experiments performed on the two binary systems sodium cholate water and sodium deoxycholate water. Implications of the presented results in the transport of lipids operated by bile salt aggregates are mentioned. The method proposed in this work, able to connect the diffusivities of an n-component system to those of the related n-1 subsystems, can be extended to obtain qualitative prediction on the diffusion coefficient trends for mixtures of other surfactants, of both industrial and biological interest.