The authors previously synthesized kynurenine by condensing o-nitrophenacyl bromide with Na phthalimidomalonic ester, saponifying the condensation product to obtain o-nitrophen-acylaminoacetic acid, the nitro group of which was then reduced to the amino group (Hoppc-Seyler''s Zeitschr. physiol. Chem. 279: 27. 1943). In the new method descr., benz-amidomalonic ester is prepared .by treating malonic ester dissolved in acetic acid with NaNO2 and converting the iso-nitrosomalonic ester formed into aminomalonic ester by hy-drogenating it with Raney nickel under pressure. The aminomalonic ester is benzoylated by treatment with benzoyl chloride in aqueous soln. in the presence of pyridine and benz-amidomalonic ester (m. 02[degree]) obtained. To 0.82 g. of Na dust is added a soln. of 10 g. of the dry benzamidomalonic ester in 80 ml. benzene. The mixture is refluxed 1/2 hr., 8.75 g. o-nitrophenacyl Br added, the mixture is refluxed 6 hrs. longer, diluted with water and shaken. The benzene layer is evaporated to dryness and the oily residue heated on the H2O bath 4 hrs. with 30 ml. concentrated HC1 and 20 ml. acetic acid. Twenty ml. HC1 are then added and the mixture heated 4-5 hrs. longer. The dark brown soln. is diluted with 120 ml. water, filtered and extracted with ether, which removes benzoic acid and unsaponifiable oils, and the aqueous, strongly acid soln. is evaporated to dryness in vacuo. The residue is recrystallized from acetone and alcohol-ether and 3.8 g. of o-nitrophenacylamiuoacetic acid hydrochloride, m. 186[degree]-187[degree], obtained. When 3.9 g. of this compound are hydrogenated with palladium black and H2SO4 added to the reaction mixture, 3.9 g. kynurenine sulfate are obtained.