An expanded bed adsorption column (5cm diameter) has been modified to allow the abstraction of liquid samples from various positions along the height of an expanded bed. As the adsorbent particles are fluidized, in-bed monitoring of protein concentration during feedstock application, washing and elution is achieved by the withdrawal of liquid samples from the voids within the expanded bed at ports along the wall of the column. Protein levels in the withdrawn streams can be assayed using on-line analytical chromatography, or samples can be collected and assayed off-line. On-line monitoring can be used to control the duration of the loading stage, or as a tool to provide information about the hydrodynamic and adsorption/desorption processes that occur during expanded bed adsorption. Breakthrough, washing and elution profiles have been monitored for a range of different adsorbate/adsorbent systems, including the adsorption of pure lysozyme on STREAMLINE SP, the adsorption of glucose-6-phosphate dehydrogenase from yeast homogenate on STREAMLINE DEAE and the adsorption of glutathione S-transferase from Escherichia coli homogenate on STREAMLINE Chelating.