A method has been presented for the simultaneous analysis of neurotoxin β-N-oxalyl-α,β-diaminopropionic acid (β-ODAP) and its non- or low-toxic isomer 0-ODAP as well as other amino acids in Lathyrus sativus extracts after derivatization with para-nitrobenzyloxycarbonyl chloride (PNZ-C1) by reversed-phase (C18 column) high performance liquid chromatography(RP-HPLC). Detection limits of isomers were 0.08 μg/mL for both β-, α-ODAP, for homoarginine 0.09 μg/mL at a signal-to-noise ratio of 3:1.