Three a-amylase producing strains of Aspergillus oryzae used for recombinant protein production have been studied with respect to growth and protein production in fed-batch and continuous cultures. The three strains are (i) a wild-type, (ii) a transformant strain of the wild-type strain containing additional copies of the a-amylase gene and (iii) a morphological mutant of the transformant strain. It is found that production of a-amylase is a growth related process. Comparison of the three strains with respect to morphology and protein production reveals that changes in the morphology of the fungus influence the a-amylase production during submerged growth.