This paper reported the radioimmunoassay for thromboxane B2 using 126I labeled tracer. The antibody against TXB2 was raised in rabbit by immunising with TXBaSA conjugate, and the 125I-histamineXB2 was prepared using the chloramine T procedure. The titre of antibody was 1:20000. The coefficient of combination of RIA was 3.9 X 109L/mol, and the accuracy, 6.5%.Its minimal detectable limit was 10 pg/mL. The normal value of adult plasma was 135.99 ?1.80 pg/mL0