We have been developing hydroxypropylmethyl cellulose (HPMC) microspheres for delivering poorly water-soluble drugs. The in vitro dissolution data showed that the presence of SDS is essential for obtaining a high level of drug release. The higher the level of drug that is released from the formulations, the greater the absorption and bioavailability of the formulation. Previous SANS data revealed some detail of the structure of the polymer-SDS complex and we have shown it is reasonable to hypothesise that the drug molecules may be encapsulated into the polymer-surfactant complex which leads to the improved dissolution of the poorly water-soluble model drug. Therefore the objectives of this proposed study are to investigate the influence of drug incorporation on the structure of the polymer-surfactant complex, and to expand the range of concentrations studied.