We studied the suppressive effect of poly-gamma-glutamate (PGA) (in the SOS response of Salmonella typhimurium induced by several direct [furylframide, AF-2; N-methyl-N-nitro-N-nitrosoguanidine, MNNG; and 4-nitroquinoline 1-oxide, 4NQO] and indirect [3-amino-1-methyl-5H-pyrido-(4,3-b) indole, Trp-P-2; 2-amino-3-methylimidazo (4,5-f) quinoline, IQ; and 2-amino-3,8-dimethylimidazo (4,5-f) quinoxaline, MeIQx] mutagens. PGA preparations with average molecular masses of 50, 2000, 4000, 6000, and 8000 kDa from Bacillus subtilis (chungkookjang) were used. When we used PGA Na salt with a molecular mass of 4000 kDa, the suppression rate increased with increasing PGA concentration; 3% PGA showed 80-90% suppression irrespective of the type of chemical mutagen. PGA preparations with molecular masses of 50 kDa and more than 6000 kDa were less effective. Glutamate and acidic polymers such as carboxymethylcellulose and xanthan gum showed lower suppressive effects than PGA. PGA proved to have high antimutagenic activity.