Despite interest in microemulsions as drug delivery vehicles, there is a lack of structural understanding to justify the formulations used. The present study examines the use of 3-(N,N-dimethyldodecylammino)-propane sulphonate (DDAPS) to stabilize oil-in-water microemulsions. We have previously used contrast variation SANS to determine the molecular architecture of DDAPS microemulsions in water. The present study aims to determine the effect of lowering pH on the structure of the aggregates. Whilst it is not possible to unambiguously determine shape using light scattering, light scattering studies ¿suggest¿ that the aggregates change from rod-like to spherical upon decreasing pH. We wish to use contrast variation SANS to study the precise nature of these shape changes as such shape changes have important implications for drug loading and release in the microemulsions.