A chromatographic technique was developed that could clearly separate beta-N [gamma-L(+)-glutamyl]-4-hydroxymethylphenylhydrazine (agaritine) from all other components in 10-500-microliters samples of mushroom extracts. Locally purchased mushrooms were found to contain mean levels of 0.4 - 0.7 mg agaritine g. The agaritine content of the mushrooms had decreased by 2-47% after 1 wk of storage in a domestic refrigerator and by 36-76% after 2 wk of such storage. Canned mushroom soup and canned mushrooms did not contain detectable agaritine; a sample of frozen mushrooms contained a mean level of 0.33 mg/g and a batch of fresh mushrooms lost about 32% of their agaritine content on cooking. In mice given 3 mg agaritine by gavage, agaritine was detected in all parts of the gastro-intestinal tract 15 min after dosing, but none was detectable in the gut after 3 hr. The enzyme gamma-glutamyltranspeptidase derived from pig's kidney was found to be capable of decomposing agaritine to glutamic acid and 4-(hydroxymethyl)phenylhydrazine, and to have nine times such activity as an enzyme isolated from mushrooms.