The field desorption mass spectra of several underivatized cyanogenic glycosides exhibit molecular ions or ions derived from the parent compound by protonation and alkali metal cationization. Abundant fragment ions are present and can be readily related to structure. Significant deviations from established fragmentation pathways are observed due to the nature of the aglycone. The ability to successfully determine the presence of cyanogenic glycosides by field desorption is demonstrated in crude extracts isolated from Vicia sativa, a food-contaminating plant material.