We propose to study the co-adsorption and interaction of a globular protein (lysozyme) with cationic surfactants in tubular silica nanopores (diameter 8 nm) using small-angle neutron scattering. At pH values well below the isoelectric point of lysozyme (pI = 11), when the protein and surfactant are both positively charged while the silica surface is negatively charged, we expect competitive adsorption of the two components and possibly displacement of preadsorbed protein by the surfactant. Closer to pI, when the net charge of the protein is low, complexation of the protein with surfactant may also occur. Preliminary results obtained in a preceding experiment at instrument D16 indicate that pre-adsorbed lysozyme can indeed be displaced from the pores of SBA-15 silica by the cationic surfactant DPC. In the proposed experiment we will investigate if and how the assembly structures in the pores are affected (1) by pH and (2) by sample preparation (pre-adsorption of protein or surfactant, etc.). The higher neutron flux of the new D16 will enable us to study relatively dilute samples in contrast-match with acceptable sensitivity.