Biodistribution of N-isopropyl-p-iodoamphetamine (IMP) was evaluated in mice. After synthesis of IMP and exchange labeling with radioactive iodine, IMP was injected intravenously in male ddY mice. Activity in the brain reached 8.0 (%dose/g), at 10 min after injection and it was almost constant till 120 min. Activities in the lung and heart were high just after injection, decreased rapidly and was almost constant from 30 to 120 min. Activity in the liver increased slowly compared with other organs, and reached peak level at 60 min. In autoradiography, almost the same activity in the spinal cord as the brain was observed. Uptake and excretion of IMP were shown in kidneys and stomach, which may be the main route of the excretion of IMP and their metabolites. We concluded IMP showed good uptake in the central nervous system.