γ-Glutamyl-S-ethenylcysteine has been isolated and crystallised from aqueous ethanolic extracts of the seeds of Narbon bean, (Vicia narbonensis). The γ-glutamyl peptide is present at 0.7% in the Australian Temperate Crops Collection cultivar ATC 60105. Depending upon genotype and environment, seeds with up to 3% peptide have been observed. This photolabile peptide is the precursor responsible for the repulsive odour of germinating Narbon beans. It is a useful chemotaxonomic character for Vicieae, as well as a significant storage form of seed sulfur.