L-Arginine-13C6,15N4 ((S)-(+)-Arginine-13C6,15N4) hydrochloride is the 13C- and 15N-labeled L-Arginine hydrochloride. L-Arginine hydrochloride ((S)-(+)-Arginine hydrochloride) is the nitrogen donor for synthesis of nitric oxide, a potent vasodilator that is deficient during times of sickle cell crisis.