Glucocorticoids are members of the corticosteroid family (the other members of this family are the mineralocorticoid group of compounds, which bind to the mineralocorticoid receptors (MR)) and are often used as anti-inflammatory and immunosuppressive agents for the treatment of diseases such as arthritis, asthma, and cancer, as well as inflammatory bowel disease and autoimmune diseases (1, 2). There is much evidence suggesting that glucocorticoids also have an important role in the development of stress, anxiety, and depression in rodents and humans by disturbing the hypothalamic-pituitary-adrenocortical (HPA) axis functions because these tissues have a high concentration of the glucocorticoid receptors (GR) (3). Normalization of the HPA function in humans is often observed during recovery from a depressive episode, and this has also been observed in preclinical studies with rats regardless of the type of antidepressant drug used to treat depression (4). It has been suggested that changes in the MR/GR balance could be responsible for regulation of the psychological stress and anxiety that lead to depression. Between the two receptors, the role of GR appears to be more clear because it has been shown that GR levels are increased during periods of anxiety, and GR activity is reduced during times of low anxiety (5). Therefore, investigators in this field believe that imaging of the GR would be an excellent technique to understand the in vivo functioning and regulation of the HPA axis. Much effort has been made to develop and evaluate fluoride ((18)F)-labeled and carbon ((11)C)-labeled GR binding radiotracers to investigate the activity and function of this receptor with the use of positron emission tomography (PET) under in vivo conditions. However, studies with these radiochemicals have had little success in delineating the function of the GR because the tracers are often metabolically unstable, have shown little penetration of the blood-brain barrier, or exhibit high non-specific binding (6). The steroid compound [N-methyl-(11)C]-(11beta17alpha)-11-[4-(dimethylamino)phenyl]-17-hydroxy-21-[4-(methylsulfonyl)phenyl]-19-norpregna-4,9-dien-20-yn-3-one ([N-methyl-(11)C]Org 34850) was reported to be a selective GR antagonist in the HPA axis with a high affinity for the receptor under in vitro conditions with the use of brain tissue homogenates (7). Because of its high potency against the GR, a (11)C-radiolabeled version of Org 34850 was synthesized by Wuest et al. to image GR in vivo and to investigate biodistribution of the radiochemical in normal rats (8).