Homologous and heterologous protein production by filamentous fungi is often limited by the expression of proteases in high levels. To overcome this problem. many strategies have been proposed including mutagenesis, gene disruption techniques or process engineering strategies. In the present study, a wild-type Aspergillus niger strain producing homologous glucoamylase was used as a model system to investigate the effect of fungal morphology on protease secretion. Morphology was manipulated by means of inoculum level and quality and characterized by image analysis. Different levels of spore inocula or vegetative inocula were used for the development of distinctive morphological forms in shake flask and bioreactor cultures. Growth of the mycelium in the form of large pellets was associated with lower specific protease activities and increased specific glucoamylase activities compared with filamentous morphologies. (C) 2002 Elsevier Science Ltd. All rights reserved.