Abstract: RS-N-isopropyl-p-iodoampheta (IMP) is radio-iodinated by isotopicexchange using Cu (I) as catalyst in presence of an excess of Sn (II) as reductor.The metod is simple and fast. A quantitative (99%) labelling yield of ~(125)I-IMPcan be obtained within 30 minutes. Free ionic ~(125)I<3%. After ether extraction,radiochemical purity is greater than 98%, free ionic ~(125)I<1%. For Biodistri-bution of ~(125)I-IMP in Spragne-Dawlay rat, the brain uptake is prompt, with1.32%/g of the injected dose reaching the brain by 5 min and peak uptake(1.49%/g) at 1h. There is a slight fall in brain activity after 3h. At all timesthe brain-to-blood ratio is more than 12. After the administration the highestradioactivity ratios of brain/blood, brain/skeletal muscle and brain/bone are17.5,5 and 9.at 30--60min respectively.