Flow-ELISA measurements of the monoclonal antibody concentration in cultivation broth containing murine hybriboma cells were carried out using a small expanded-bed column (0.5x2.5 cm) charged with protein A. A new specialised pellicular agarose/stainless steel matrix designed for high flow rates with fast mass transport properties was used. Special care was taken to get an efficient flow distribution. The axial dispersion coefficient was very low (2x10(-6) m(2) s(-1) for latex particles at a linear velocity of 10 cm min(-1)). Breakthrough curves for polyclonal IgG on the protein A-derivatised support (at 2-11 cm min(-1)) further emphasised its advantageous properties. No significant change in dynamic capacity was found over the entire speed range.