Although microemulsions have been widely investigated as potential drug delivery vehicles, relatively 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 menthol and the drug lidocaine as the oil to prepare a pharmaceutically acceptable microemulsion. 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 proposed study forms an integral part of a large on-going project in our laboratory investigating the potential of surfactant and lipid aggregates as drug delivery vehicle