Liquid pharmaceutical formulations are commonly comprised of proteins and surfactants, which interact in solution in order to provide an increase in system stability. Although these systems have been significantly investigated in the last few years, there is a lack of consensus concerning the interaction mechanism between proteins and surfactants. We believe that contrast variation small-angle neutron scattering can provide specific information about these systems and contribute to resolving the puzzle. In this experiment we aim to elucidate the interactions between human growth hormone and a prototypical anionic amphiphiles at room temperature. The use of isotope labelling and contrast matching will provide detailed information about individual parts of the system, which will then be co-refined in order to provide structural information of the protein-surfactant complexes as a whole.