Lathyrism, a form of motoneuron disease induced by excessive consumption of th legume Lathyrus sativus (chickling pea), presents as signs of pyramidal tract involvement. Primate feeding studies show that beta-N-oxalylamino-L-alanine (BOAA), a potent neuroexcitatory aminoacid in the chickling pea, induces corticospinal dysfunction similar to that seen in animals consuming a fortified diet of this legume. BOAA, a potent agonist of the excitatory neurotransmitter glutamate, is likely to be causally associated with lathyrism in man.