The chemical structures of the metabolites induced in oat leaves that had been inoculated with an incompatible race of crown rust fungus (phytoalexins) were examined. An HPLC analysis, using synthetic standards, demonstrates that they were a series of N-acyl 5-hydroxyanthranilates named avenanthramides, where the acyl groups were p-coumaroyl (avenanthramide A), feruloyl (avenanthramide B), and 5-(4′-hydroxyphenyl)-penta-2, 4-dienoyl (avenanthramide L).