Agaricus blazei MURRILL mushroom products are sold as so-called health foods in Japan. However, a part of Agaricus is known to contain hydrazines. A sensitive and specific method for analyzing a genotoxic hydrazine, agaritine, and its derivatives was developed to assess the safety of Agaricus products. β-N-(γ-L(+)-Glutamyl)-4-(hydroxymethyl)phenylhydrazine (agaritine, AGT), 4-hydrazinylbenzylalcohol (HMPH), 4-hydrazinylbenzoic acid (CPH), 4-methylphenylhydrazine (MPH) and phenylhydrazine (PH) were converted to their correspond-ing fluorescent derivatives with 3,4-dihydro-6,7 dimethoxy-4-methyl-3-oxoquinoxaline-2-carbonyl chloride (DMEQ-COCl) as the fluorescence derivatization reagent. The detection limits (S/N=3) for CPH, AGT, PH and MPH were 422, 45.3, 16.5 and 138 fmol, respectively, in a 20 μl injection volume. Recoveries, achieved by adding known AGT amounts to the Agaricus sample and Agaricus products, ranged from 92.8 to 102%. By using this method which does not require partial purification of the Agaricus sample, the amounts of AGT in several types of foods were found to be 112—1836 μg/g dry weight.