Tritiated L-arginine was prepared by catalytic exchanging in tritiated aqueous medium. The tritiated water of high activity was prepared by the reaction of PtO

2

and tritium gas in acetic acid medium. The mixture of L-arginine

solid catalyst(10% Pd/C)and acetic acid containing tritiated water was sealed in a small glass vessel

then heated at 120℃ for 6h. After reaction

the tritiated water and acetic acid as well as catalyst were removed. The crude product was purified by paper chromatography. The specific activity of the product was 778mCi/mmol (28.8GBq/mmol) with radiochemical purity over 96%.