Adsorption of a globular protein on a hydrophilic solid/liquid interface was investigated. Neutron reflectivity was used to determine structural information on an adsorbed beta-lactoglobulin layer at a hydrophilic silicon surface. The thickness of the protein film was found to be compatible with the diameter of the native protein, indicating that possible conformational changes of the protein during adsorption are not gross enough to alter the shape of the protein. The amount adsorbed is consistent with that derived by our ellipsometry measurements, obtained in similar experiments. Evidence for significant H-D exchange in the adsorbed protein was found. Copyright 1999 Academic Press.