Abstract: Abstract: AIM: To establish the method and investigate the pharmacokinetics and distribution of 125I-rhTPO in mice receiving caudal vein injection. MEHTODS: 125I-rhTPO was radio-iodinated by Iodogen solid labeling method, and was isolated and purified by Sephadex-G25 agarose. The radiochemical purity of labeled protein was analyzed by paper chromatography. After caudal vein injection with 125I-rhTPO, the plasma samples were collected at different time and the drug concentration was determined according to the radioactivity. Then the pharmacokinetic parameters were calculated. The distribution of 125I-rhTPO in mice was measured at different times after caudal vein injection with 125I-rhTPO. RESULT AND CONCLUTION: It is shown that the labeling rate of 125I-rhTPO was 96.25%, radiochemical purity is 95.85%. The pharmacokinetics of 125I-rhTPO following i.v. with 1g.kg-1 in mice was fit to two-compartment model, T1/2 was 0.30h，T1/2 was 6.20h. The distribution of 125I-rhTPO in different tissues showed that most of the 125I-rhTPO was metabolized by the kidney, a little of the 125I-rhTPO was metabolized by the liver and gall system. The radioactivity level in breastbone was higher than in thighbone and shinbone, the radioactivity level in shinbone was the lowest. It is suggest that the bone marrow was the target of the rhTPO.