Like other members of the TNF family, TRAIL/Apo‐2 ligand induces apoptosis in sensitive target cells in a caspase‐dependent fashion. We recently found that TRAIL may be constitutively expressed on the surface of mouse and human tumor cells of T and B origin. To define the pattern of TRAIL expression in normal immune cells, freshly isolated splenocytes, Concanavalin A/IL‐2‐activated T cells and lipopolysaccharide‐activated B cells were analyzed by surface staining with or without secondary stimulation. Activated, but not resting, CD3⁺ cells expressed TRAIL in an activation‐dependent fashion. Conversely, freshly isolated B220⁺ cells displayed surface TRAIL and CD95L that were retained following activation. Restimulation with the protein kinase C activator phorbol 12‐myristate 13‐acetate and the calcium ionophore ionomycin or an agonistic anti‐CD3 monoclonal antibody induced significant up‐regulation of surface TRAIL and CD95L in CD3⁺ , TCRα β cells with CD4⁺ or CD8⁺ phenotype. Similarly to CD95L, TRAIL up‐regulation was protein synthesis dependent and cyclosporin A sensitive. These results indicate that both TRAIL and CD95L are displayed on the cell surface of activated immune cells and may thus represent complementary effector pathways in the regulatory functions of T and B cells.