An iodine 123-radiolabled small molecule that exhibits high affinity for prostate-specific membrane antigen (PSMA) with potential use in molecular imaging. Iofolastat I123, a radiolabeled glutamate-urea-lysine analogue, selectively binds PSMA, which allows imaging of PSMA-expressing prostate cancer cells with gamma scintigraph. PSMA is a transmembrane glycoprotein highly expressed by malignant prostate epithelial cells and vascular endothelial cells of various solid tumors.