Abstract: Experimental results of three rapid labelling methods, namely, hydrothermal melting method, melting method and crown ether method are described. Our results indicate clearly that the hydrothermal melting method gives the highest labelling efficiency, radiochemicalContinued on P.135) purity (radioiodohippuran above 99%, radioiodide about 0.3-0.5%, radiobenzoic acid less than 0.2%) and simplicity. The product of hippuran can be used directly for clinical purposes.Reaction temperature,time dependance and pH values of initial material are investigated, and optimum condition are: temperature, 152-156℃; reaction time, 20 min; pH value, 1-2. The mechanism of isotopic exchange reaction is also studied.