We show that expanded bed protein A affinity chromatography using Streamline rProtein A. media is an efficient method for purifying a recombinant humanized monoclonal antibody from unclarified Chinese hamster ovary cell culture fluid and that it provides purification performance comparable to using a packed bed. We determined that the dynamic capacity of the expanded bed media is related to flow rate (measured in column volumes per hour) by a power function, which allows a high capacity at a low flow rate. At 250 cm h(-1) with a 25 cm bed height (10 column volumes h(-1)), the dynamic capacity is 30 g l(-1). The yield and purity (measured by the amount of host cell proteins, DNA, SDS-PAGE, and turbidity) of the antibody purified by expanded bed is comparable to the yield and purity obtained on a standard packed bed method using Prosep A media. (C) 1999 Elsevier Science B.V. All rights reserved.