Abstract: In this paper, thromboxane B₂ (¹²⁵I)-RIA. The quality of TXB₂ antiserum was xcellent. The affinity constant of TXB₂ antiserum was 2.4×10¹⁰L/mol. Investigator xpressing the accuracy of the method was determined to be 94.7—106.0%. Variation coefficency f the assay in batch and between was 6.4% and 11.8% respectively. Assay range of standard urve o be 2.5—160.0 pg per tube. The concetration value of the normal plasma and urine was 143.5 8.8 pg/ml and 229.9 ± 14.4pg/min respectively. The specimen assay and compared with TXB₂ （~125）I)-RIA and TXB₂ （~3H）-RIA. The correlativety was excellent （r =0.808）.The changes of TXB n persons taken aspirin and patients suffered from coronary heart disease, myocardial nfarction and uremia were discussed briefly.