The microstructure of the quaternary water-in-oil microemulsion CTAB/water/n-pentanol/n-hexane has been investigated by means of the pulsed gradient spin-echo NMR technique over a wide range of composition. The composition of the continuous organic phase and of the interracial phase has been determined through the analysis of the n-pentanol self-diffusion coefficient. The size of the reverse aggregates has been evaluated from the CTAB self-diffusion coefficient. The correlation of the reverse micellar size with interfacial composition has therefore been possible. Results coming from both water dilution lines and interface dilution lines have been analyzed according to suitable models. A "master plot", i.e., a graphical representation that allows us to display the data collected at all the possible compositions of the four components system, is also proposed.