Abstract3‐(1,2,5,6‐Tetrahydro‐4‐pyridyl)‐5‐pyrrolo[3,2‐b]pyridone, CP‐93, 129, is a selective agonist ligand for 5‐HT1Breceptors. High affinity binding sites of [3H]CP‐93, 129 were found in rat whole brain membranes, which showed KDand Bmaxvalues similar to those for 5‐HT1Bsites labeled by [3H]5‐HT. Uptake of [3H]CP‐93, 129 in crude rat synaptosomes was also observed, which was potently inhibited by 5‐HT uptake blockers and 5‐HT but not by desipramine (NE uptake blocker) or tametraline (NE and DA uptake blocker). Because of this sensitivity to 5‐HT uptake inhibitors and the structural similarity of CP‐93, 129 to serotonin, [3H]CP‐93, 129 uptak