The central nervous system (CNS) dopaminergic system in mammalian brain is very important for normal brain function and is the action site for neuroleptic drugs in treating schizophrenia and other mental disorders. Cloning of dopamine receptors has yielded at least six subtypes (D1, D2L, D2s, D3, D4, D5), with D3 differing from D1/D2 in amino acid sequence, pharmacological profiles, tissue distribution, and receptor-effector coupling mechanisms. The lack of potent, selective ligands with high specific activity hinders understanding D3's function. Recently, [3H]-7-OH-DPAT was identified as a selective D3 ligand (Kd = 0.67 nM in CHO cells). Based on this, we designed an iodinated derivative, (R,S)-2'-trans-7-hydroxy-2-[N-n-propyl-N-(3'-iodo-2'-propenyl)amino]tetralin (trans-7-OH-PIPAT, 5), by placing iodine on the N-propenyl side chain, resulting in a stable compound with higher specific activity (2200 Ci/mmol for 125I), selectivity, binding affinity, and lower nonspecific binding. Synthesis of trans-7-OH-PIPAT (5) was achieved via a reaction sequence. Binding studies with D2/D3 receptors expressed in Sf9 cells showed trans-7-OH-PIPAT is highly selective for D3 (Ki D2/D3 ratio = 143). [125I]-trans-7-OH-PIPAT displayed saturable, high specific binding (nonspecific ~10% at Kd) with one-site binding (Hill coefficient ~1) and Kd = 0.13 nM. Competition experiments revealed known D2/D3 ligands have high D3 affinity, while D1 and other receptor ligands have moderate/low affinity. In conclusion, we report the synthesis and initial binding characterization of trans-7-OH-PIPAT, the first novel iodinated D3 dopamine ligand. It demonstrates high affinity and selectivity for D3 and may be used to study D3 receptors in vivo/in vitro, aiding understanding of D3 pharmacology and its relevance to neuroleptics for mental illness treatment.