This work demonstrates an experimental method for studying breakthrough behaviour in expanded beds. The behaviour of beds made with differently sized particles were studied at varying flowrates. The use of a dimension-less residence time measurement allowed a more valid comparison of breakthrough characteristics in expanded bed operation by compensating for the changes in bed volume that occur during expansion. We demonstrate that bed breakthrough behaviour can be compared directly even when the beds contain different-sized particles and hence have different expanded volumes. By utilising this concept we demonstrate that, in the case of the Alcohol Dehydrogenase (ADH) / STREAMLINE Phenyl system used here, there was little or no variation in ADH breakthrough behaviour between beds of differently sized particles operating at flowrates above 100 cm/h. This suggests that the higher specific surface area and hence binding capacity of smaller particles is negated in this case due to mass transfer limitations and the increase in system void volume even at normal operating flowrates of 200-300 cm/h. (C) 2004 Wiley Periodicals, Inc.