We report the synthesis and evaluation of 1′4125Iiodobenzyl3Hspiroisobenzofuran1,4′piperidine 125ISpiroI as a potential SPECT tracer for imaging of σ1receptors. 125ISpiroI was prepared in 55–65 isolated radiochemical yield, with radiochemical purity of >99, via iododestannylation of the corresponding tributyltin precursor. In receptor binding studies, SpiroI displayed low nanomolar affinity for σ1receptors σ1: Ki2.75±0.12 nM; σ2: Ki340 nM and high subtype selectivity σ2σ1124. Biodistribution in mice demonstrated relatively high concentration of radioactivity in organs known to contain σ1receptors, including the lung, kidney, heart, spleen, and brain. Administration of haloperidol 5 min prior to injection of 125ISpiroI significantly reduced the concentration of radioactivity in the abovementioned organs. These findings suggest that the binding of 125ISpiroI to σ1receptors in vivois specific. Copyright © 2010 John Wiley & Sons, Ltd.