An experiment was conducted to elucidate the mechanism of the regulation of beta-amylase synthesis in Bacillus acidopullulyticus NCIMB11608. It was found that the synthesis of beta-amylase was induced by starch and repressed by glucose. beta-Amylase derepressed mutants of B. acidopullulyticus NCIMB11608 were isolated by nitrosoguanidine mutation, using a starch medium containing 2-deoxyglucose as a repressor for the catabolite repression-resistant mutants. One promising mutant, designated as CR27-9-2, was selected which possessed five times the beta-amylase activity of its parental strain. It was also found that the differential rate of enzyme synthesis in mutant CR27-9-2 was constant, regardless of the presence or absence of starch. Therefore, it was concluded that the synthesis of beta-amylase in mutant CR27-9-2 was both constitutive and catabolite repression-resistant. In addition, CR27-9-2 was also catabolite repression-resistant for the synthesis of other amylolytic enzymes, such as alpha-amylase, pullulanase, and glucoamylase.