A neuroactive principle of Lathyrus latifolius has been isolated in crystalline form as a monohydrochloride and has been identified as L-alpha,gamma-diaminobutyric acid. This amino acid has also been found in very high concentration in the toxic seed of Lathyrus sylvestris Wagneri. A structural relationship between this factor, the lathyrus factor from Lathyrus odoratus, and, beta-cyano-L-alanine, a new, synthetic neuroactive amino acid nitrile, is pointed out, and a possible biosynthetic pathway relating these is indicated.