The binding characteristics of the σ ligand [ 3 H]1,3-di(2-tolyl)guanidine (DTG) were investigated in membranes prepared from the Jurkat T cell line. Binding was saturable with a K D of 56 ± 3 nM and a B m a x of 11706 ± 3173 fmol/mg protein (n = 3). The rank order of potency for σ reference compounds to inhibit binding in the Jurkat cell line was ifenprodil > 1,3-di(2-tolyl)guanidine > haloperidol > carbetapentane > (+)3-(3-hydroxyphenyl)-N-propylpiperidine ((+)3-PPP) > (-)pentazocine > caramiphen > (+)pentazocine, and significantly correlated with potency at σ 2 binding sites in guinea pig brain (r = 0.90, p < 0.01). The immunomodulatory activities of the σ ligands 1,3-di(2-tolyl)guanidine, haloperidol, (-)pentazocine and (+)pentazocine on CD3-induced proliferation, IL-2 production and Ca 2 + flux in human lymphocytes did not reveal any consistent pharmacology that could be ascribed to potency of these compounds at σ binding sites. Collectively the data demonstrate that the [ 3 H]1,3-di(2-tolyl)guanidine binding site on Jurkat cell membranes has a pharmacology consistent with σ 2 receptors, but no modulation of functional activity or intracellular events in human peripheral blood lymphocytes correlating with σ receptors was found.