Movement towards or away from a given stimulus guides the directional migration of prokaryotes, simple eukaryotes and neurons. As bi-directional cues may influence entry and exit of immune effector cells from tissue sites, we evaluated the migratory responses of T-cell subsets to varying concentrations of the chemokine stromal cell derived factor-1 (SDF-1). There was selective repulsion of subpopulations of T cells at high concentrations of recombinant SDF-1 or naturally occurring bone marrow-derived SDF-1, which could be inhibited by pertussis toxin and antibody against the chemokine receptor CXCR4. Distinct sensitivity profiles to genistein, herbimycin and 8-Br-cAMP biochemically distinguished movement of cells towards or away from an SDF-1 gradient. In vivo, antigen-induced T-cell recruitment into the peritoneal cavity was reversed by high but not low concentrations of SDF-1. The phenomenon of movement away from a chemokine represents a previously unknown mechanism regulating the localization of mature T cells. It adds to the functional repertoire of chemokines that may participate in immune physiology and may be applied therapeutically to alter the immune response.