By using 2-deoxy-D-glucose, selection of different mutants of Aspergillus oryzae PTCC 5164, which were produced by random mutagenesis by u.v. radiation, nitrous acid and N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), was studied. 2-Deoxy-D-glucose, a well-known antimetabolite, was used to isolate derepressed mutants. The mutational and lethal effects of these mutagens on conidia of A. oryzae were compared and the frequency distribution of isolated mutants, in the presence of 2-deoxy-D-glucose, was determined. Potent mutants, which produced higher dextrinizing and saccharogenic activities, were isolated. The best strain was a result of mutagenesis by nitrous acid, which produced 6.73 times more dextrinizing and 5.13 times more saccharogenic activity than the parent strain. In general, the mutants obtained by nitrous acid and u.v. were more potent than those obtained by MNNG.