Abstract: A rapid method is described for the labelling of 1-bromohexadecane with 125I and 82Br in the presence of crown ether which is used as a solvent. Benzo-12-crown-4, 15-crown-5, 18-crown-6 and 24-crown-8 are chosen as crown ethers because of its low melting point, In an isotopic exchange between 1-bromohexadecane and 125I and 82Br, the substrate and radioactive alkali halides are dissolved in the crown ether solvent. The unsolvated and "naked radioactive anions" have more reactive ability than those in the conventional condition. Our results show that there is a great crown ether effect in the halogen atom exchange or isotopic exchange. The time dependence of 1-bromohexadecane with 125I and 82Br and kinetics of isotopic exchange reactions in the benzo-12-crpwn-4 medium are studied, and the velocity constants of reaction from half-life of exchange reaction at various temperatures obtained. The activation energy of these isotopic exchange reactions is calculated from a plot where the velocity of reaction against the reciprocal temperature is a straight line. The effects of cations (Li+, Na+, K+) complexed with benzo-12-crown-4 and 15-crown-5 in exchange reaction are also examined.