A series of analogues of the potent and selective sigma receptor ligand 1,3-ditolylguanidine (DTG) were synthesized and demonstrated to have high affinity for the sigma receptor as measured by in vitro [3H]DTG displacement studies using guinea pig brain tissue. Three of these 1-aryl-3-(1-adamantyl)guanidines were radiolabeled--two with carbon-11 and one with fluorine-18. Radiochemical yields and specific activities were sufficient for these radiotracers to be used in positron emission tomography imaging of the haloperidol-sensitive sigma receptor.