Technical Abstract: Medicago sativa 'G98A' is highly resistant to the potato leafhopper, Empoasca fabae. Glandular trichome extracts from G98A were fractionated using flash chromatography and tested for settling deterrency against the potato leafhopper. A fraction of intermediate polarity was strongly deterrent when applied to the surface of an artificial diet sachet. But, deterrency was not detected when contact was limited to only the leafhoppers' stylets. Gas chromatography-mass spectrometry determined major components of the highly deterrent fraction were a series of fatty acid amides with free fatty acids as minor components. Deterrency slightly declined, but was still strong, after fatty acids were removed from crude extracts. When the crude extracts were separated further, a fraction containing only the fatty acid amides was also deterrent. Activity increased when this fraction was supplemented with authentic (C12-C18) free fatty acids. However, the authentic free fatty acids were not deterrent when tested without the lipophilic amides. Fatty acid amides and free fatty acids in trichomes of M. sativa G98A may together function in deterring settling by the potato leafhopper.