The y-glutamyl derivative of B-(isoxazolin-S-on-2-yl)-alanine was found in seedlings of Lens culinaris and Luthyrus sativus. The chemical and spectroscopic properties are compared with its decarboxylation product previously found in seedlings of Lathyrus odoratus. NMR studies of the two derivatives indicate the absence of cyclization and the probability of cis-trans isomers. Some biochemical implications related to potential ways to detoxify Lnthyrus satiuus are discussed.