Aspergillus niger has a long history of commercial usage as a host for the production of both homologous and heterologous secreted proteins. Nonetheless, heterologous proteins are poorly expressed compared to some homologous proteins.  Endogenous proteases and competition with native secreted proteins for rate limiting steps in the secretory pathway are thought to be major contributing factors.  Previously, in an effort to reduce the total amount of secreted native proteins we constructed an Aspergillus niger strain with the gene coding for the major secreted protein, glucoamylase, deleted.  In this study, we continue our efforts to improve the expression of heterologous proteins by deleting four additional genes. We first deleted the argB locus in order to have an additional selection marker. Subsequently, a 13013 bp region of Chromosome VI that codes for three genes, prtT, encoding the transcription regulator for the major secreted proteases pepA and pepB, amyA encoding the acid a-amylase, and aglU encoding an a-glucosidase was replaced by a 159 bp fragment. Total acidic and neutral protease and a-glucosidase activity expressed by the resulting strain was reduced by 90%. This deletion also significantly reduced amylase expression. Finally, the resulting strain expressed three test proteins at similar levels to that obtained by the parent strains, N593 and RS6122; however, the specific activity of the expressed enzymes in the culture filtrates were increased due to the reduced production of secreted proteins.