McN-5652 is one of a series of substituted pyrrolo-isoquinolines that, as a group, potently inhibit the uptake of one or more of the monoamines, norepinephrine, serotonin and dopamine. Receptor binding experiments indicated that McN-5652 has a weak affinity for serotonin 5-HT2 and alpha-1 adrenergic receptors. Abnormalities of the 5-HT transporter have been suggested in mood disorders, since it is one of the major binding sites of antidepressants. (+)-[11C]McN 5652 is an appropriate radiotracer to quantify 5-HT transporters in regions with relatively high concentration of 5-HT transporters, such as the midbrain, thalamus, and basal ganglia, and should prove useful in elucidating abnormalities of 5-HT transmission in neuropsychiatric conditions.