A radiopharmaceutical, (123)I-labeled 2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine ([(123)I]ADAM), has been developed recently for evaluation of how serotonin transporters (SERT) function in the brain. However, the detailed biodistribution and specific binding in certain brain areas are not well investigated. In this study, both phosphor plate imaging and microautoradiography were applied to explore the binding characteristics of [(123)I]ADAM in SERT neurons. The effect of two psychotropics and one narcotic on the binding of [(123)I]ADAM to SERT was also studied. Fluoxetine and desipramine, both are psychotropics and specific SERT ligands and decreased the affinity of [(123)I]ADAM, while p-chloroamphetamine (PCA), a narcotic, destroyed most of serotonergic neurons, as well as reducing the concentration of serotonin and the number of SERT in the brain as shown by the biodistribution of [(123)I]ADAM. Significant and selective accumulation of [(123)I]ADAM in the areas from midbrain to brain stem in normal mice with maximum target-to-background ratio was found at 90 minutes postinjection. A rapid clearance of [(131)I]ADAM at 120 minutes postinjection was found in the CA1, CA3 and ThN brain areas. In addition, the inhibition effect on binding ability of [(123)I]ADAM to SERT by the psychotropics and the narcotic was found to have the order of: PCA > fluoxetine > desipramine.