Abstract: The tissue distribution and pharmacokinetics of 125I labeled p-iodophentermine (¹²⁵I-IP) as a brain perfusion imaging agent in SD rats was studied and compared with those of the other two 125I labeled amine brain imaging agents ¹²⁵I-IMP (N-isopropyl-4-iodoamphetamine) and ¹²⁵I-HIPDM [N, N,N'-trimethy 1-N'-(2-hydraxy-3-methyl-5-iodobenzyl)-l，3-propanediamine]. The results showed that the lipo-philicity of ¹²⁵I-IP is increased by substituting, with methyls, which makes the agent easier to pass through the blood-brain barrier.