Although microemulsions have been investigated as potential drug delivery vehicles, little work has been performed establishing the detailed molecular architecture of the drug-containing microemulsions. The present study uses the novel approach of using a eutectic mixture of two local anaesthetics namely menthol and lidocaine, as the free base, as the ¿oil¿ to prepare a pharmaceutically acceptable microemulsion suitable for anesthesia of the mouth or the skin. Small angle neutron scattering measurements in combination with contrast variation will be used to determine the location of the eutectic mixture in the microemulsion as a function of composition and surfactant (either dodecyldimethylammoniopropane-sulfonate, sodium dodecyl sulphate or dodecyl trimethyl ammonium bromide). The study is part of on-going project in our group investigating microemulsions as drug delivery vehicles.