Filamentous fungi such as Aspergillus niger, Aspergillus oryzae, and Trichoderma reesei are able to produce and secrete large concentrations of enzymes (e.g. amylases, proteases, cellulases) into the environment. Increasingly, these species and a few others are being used to produce recombinant proteins, particularly proteins of fungal origin (Table 1). For producing recombinant proteins (which may be a protein which the host organism already makes, i.e. an homologous protein, or a new, i.e. heterologous, protein), filamentous fungi offer the advantages of possessing an efficient secretion system, being able to glycosylate proteins and having higher specific growth rates than plant, insect or mammalian cells. Although the filamentous growth form causes more difficulties for mixing and aeration than does the unicellular growth form of yeast and bacteria, efficient fermentation technologies have been developed for antibiotic, organic acid and native enzyme production from filamentous fungi.