The predominant glucosinolate in the crucifer Lepidium sordidum A. Gray is shown to be 3,4,5-trimethoxybenzylglucosinolate (III), not previously encountered in Nature, but present also in L. hyssopifolium Desv., and characterized as a crystalline potassium tetraacetate. The identification is based on chemical and enzymic hydrolysis, the latter producing 3,4,5-trimethoxybenzyl isothiocyanate (II), indistinguishable from a synthetic specimen. The natural occurrence of ring-oxidized benzylglucosinolates is briefly discussed.