NEW MATERIAL: δ-sbstd. ornithine derivative of formula I (wherein R is -CH2F, -CHF2, -CHClF, -C≡CH, -CH=CH2, -CH=C=CH2) or its acid-added salt.

EXAMPLE: 2,5-diamino-6-fluorohexanoic acid (δ-fluoromethyl-ornithine).

USE: An inhibitor for L-ornithine: 2-oxo acid aminotransferase which is an enzyme of mitochondria existing in the liver, the ren, the brain, etc., and being useful as a treating agent for diseases and symptons characterised by temporary shortage of ornithine. The symptons which bring about temporary shortage of ornithine are hepatotoxin, hepatic insufficiency, gastro-intestinal tract hemorrhage, hereditary urea cycle disease, etc.

PROCESS: After a compd. of formula II is reacted with a Grignard's reagent prepd. of a compd. of formula III (wherein p is a hydroxy protective group; X is chloro, etc.), it is reduced with sodium borohydride to obtain a compd. of formula I.