The effect of glucose on the alpha-amylase production by Bacillus subtilis ATCC-21556 was studied. Initial glucose concentrations up to 20 g/L were found to be directly proportional to the specific alpha-amylase production in an immobilized-cell batch system, whereas a free-cell batch system presented an inversely proportional relationship with the initial glucose concentration. This might be owing to the alpha-amylase repression by the glucose present in the culture medium. Three hundred eighty-five percent of the specific a-amylase production with the free-cell system was produced by the immobilized-cell batch culture.