Isotope substitution is currently used by several techniques such as small-angle neutron scattering (SANS), electron spin echo modulation (ESEM), and nuclear magnetic resonance (NMR), which are able to provide information at a molecular level. This substitution was found to produce changes in several physical processes (i.e., phase transitions, coexistence curves, critical phenomena, etc.). The effect of the isotope substitution and in particular the effect of perdeuteration of a component is not fully understood yet, and in some cases, contradictory results have been obtained. This paper reports a quasi-elastic light-scattering (QELS) study of water/oil microemulsions in which water, oil, and alcohol have been selectively deuterated. The results show that selectively deuterated microemulsions are similar to non-deuterated ones, in agreement with the fact that the phase diagram is not dramatically changed. The microemulsion droplets have a radius of about 100 Angstrom, and the interdroplet interactions can be described by a hard-sphere repulsion potential and an attractive term due to Van der Waals interactions. The salinity has a similar role for;both deuterated and non-deuterated microemulsions. Higher salinities favor higher curvatures. Changes in the hydrodynamic radius and in the second virial coefficient of the interdroplet interaction potential are found upon deuteration of different regions of the microemulsions.