sigma 1 receptor ligands have potential pharmacological significance as antipsychotic drugs, as tools in the study of drug-induced motor function disorders, and as radiopharmaceutical imaging agents for the noninvasive imaging of malignant tumors in human subjects. A series of substituted N-benzyl-N-normetazocines were synthesized and their binding affinity at the sigma 1 receptor evaluated in order to examine the details of the structure--affinity relationships (SAR) of a previously determined high-affinity lead compound, (+)-cis-N-benzyl-N-normetazocine (Ki = 0.67 nM). Variation in the benzyl substituents of these compounds produced a 1590-fold range in affinity at the sigma 1 receptor from the unsubstituted benzyl analog to the lowest affinity p-tert-butylbenzyl analog (Ki = 1066 nM). The nanomolar binding affinity for the sigma 1 receptor of (+)-cis-N-(4-fluorobenzyl)-N-normetzocine suggests that this analog may be a useful PET imaging agent.