Abstract: Recent studies indicate that sigma receptors are a class of non-opiate, non-dopaminergic proteins. The structure, physiological and biochemical functions, and the pharmacological significance of sigma receptors are not completely understood. A wide variety of human tumors, including malignant melanoma, non-small cell lung carcinoma,tumors of breast, prostate, colon, kidney, and neural origin contain a high density of sigma receptors. Therefore, the development of high affinity sigma receptor-specific radio-ligands has become an attractive target.The radio-ligands not only can be used to study the physiological and biochemical functions and pharmacology of sigma receptors, but also can be potentially used to image and treat sigma receptor-positive tumors.