Abstract: STUDY ON  125 I LABELING OF CEREBROLYSIN AND ITS BIODISTRIBUTION IN MOUSEYan Ping\ Ni Xiuxiong *\ Lin Min *\ Wang Zhongzhou *\ Huang Qingzhong\ Zhuo Ruo * (Department of Nuclear Medicine, Fujian Medical University, Fuzhou 350004) (*Department of Pathological Physiology, Fujian Medical University, Fuzhou 350004) ABSTRACT Cerebrolysin is labeled with  125 I using the method of Chloramine T. The labelled yield is (32.5±5.0)% ( n =3) and the specific activity of the labeling product is 1.98 TBq/g. By the method 20% trichloroacetic acid precipitation, the radiochemical purity of the purified  125 I cerebrolysin is more than 90% and descent of radiochemical purity in a week is less than 5%. The results of biodistribution of  125 I cerebrolysin in mouse show that cerebrolysin can pass through blood brain barrier and its remaining time in brain is longer relatively than that in other tissues. It suggests that the brain have a function of taking up  125 I cerebrolysin. Key words\ cerebrolysin\  125 I labeling\ biodistribution