THE nuclear magnetic resonance (NMR) and mass spectra of the novel amino acids (IV) and (V) isolated from Aesculus californica by Fowden and Smith (preceding paper) have been determined. These spectra provide very strong evidence for the formulation of these amino acids as 2-amino-6-hydroxy-4-methylhex-4-enoic acid (IV) and 2-amino-3-(methylenecyclopropyl)butyric acid (α-methyl-β-(methylenecyclopropyl)alanine) (V).