This is the first demonstration of process scale-up of a membrane gradostat reactor for continuous enzyme production using Phanerochaete chrysosporium ME446. The fungus was immobilised by reverse filtration on to externally unskinned, ultrafiltration capillary membranes and then nutrient gradients were induced across the biofilm. A 10-fold scale-up from a single capillary bioreactor to a 2.41 multi-capillary unit resulted in a 7-fold increase in enzyme productivity with a peak at 209 U l(-1) d(-1). Subsequent scale effects on the spore distribution, continuous manganese peroxidase production profile and biofilm development are discussed.